MUROS modulation using linear baseband combinations with linear gaussian pulse shaping for two users on one timeslot used by non-DARP and DARP remote stations

ABSTRACT

The present patent application improves DARP by allowing multiple users on one time slot (MUROS). It comprises means, instructions and steps for combining two signals. In one example, it comprises at least one baseband modulator, a plurality of amplifiers where the signals are multiplied by a gain; at least one combiner operably connected to the amplifiers where the signals are combined; and a phase shifter where one of the signals is phase shifted with respect to the other signal. In another example; the apparatus further comprises a phase shifter operably connected to the at least one baseband modulator to provide a π/2 phase shift between the two signals. In another example, the at least one baseband modulator comprises a BPSK baseband modulator on an I axis and a BPSK baseband modulator on a Q axis.

FIELD OF THE INVENTION

The invention relates generally to the field of radio communications andin particular to the increasing of channel capacity in a radiocommunications system.

BACKGROUND

More and more people are using mobile communication devices, such as,for example, mobile phones, not only for voice but also for datacommunications. In the GSM/EDGE Radio Access Network (GERAN)specification, GPRS and EGPRS provide data services. The standards forGERAN are maintained by the 3GPP (Third Generation Partnership Project).GERAN is a part of Global System for Mobile Communications (GSM). Morespecifically, GERAN is the radio part of GSM/EDGE together with thenetwork that joins the base stations (the Ater and Abis interfaces) andthe base station controllers (A interfaces, etc.). GERAN represents thecore of a GSM network. It routes phone calls and packet data from and tothe PSTN and Internet and to and from remote stations, including mobilestations. UMTS (Universal Mobile Telecommunications System) standardshave been adopted in GSM systems, for third-generation communicationsystems employing larger bandwidths and higher data rates. GERAN is alsoa part of combined UMTS/GSM networks.

The following issues are present in today's networks. First, moretraffic channels are needed which is a capacity issue. Since there is ahigher demand of data throughput on the downlink (DL) than on the uplink(UL), the DL and UL usages are not symmetrical. For example a mobilestation (MS) doing FTP transfer is likely to be given 4D1U, which couldmean that it takes four users resources for full rate, and eight usersresources for half rate. As it stands at the moment, the network has tomake a decision whether to provide service to 4 or 8 callers on voice or1 data call. More resources will be necessary to enable DTM (dualtransfer mode) where both data calls and voice calls are made at thesame time.

Second, if a network serves a data call while many new users also wantvoice calls, the new users will not get service unless both UL and DLresources are available. Therefore some UL resource could be wasted. Onthe one hand, there are customers waiting to make calls and no servicecan be made; on the other hand, the UL is available but wasted due tolack of pairing DL.

Third, there is less time for mobile stations (also known as UserEquipment or UE) working in multi-timeslot mode to scan neighbor cellsand monitor them, which may cause call drops and performance issues.

FIG. 1 shows a block diagram of a transmitter 118 and a receiver 150 ina wireless communication system. For the downlink, the transmitter 118may be part of a base station, and receiver 150 may be part of awireless device (remote station). For the uplink, the transmitter 118may be part of a wireless device, and receiver 150 may be part of a basestation. A base station is generally a fixed station that communicateswith the wireless devices and may also be referred to as a Node B, anevolved Node B (eNode B), an access point, etc. A wireless device may bestationary or mobile and may also be referred to as a remote station, amobile station, a user equipment, a mobile equipment, a terminal, aremote terminal, an access terminal, a station, etc. A wireless devicemay be a cellular phone, a personal digital assistant (PDA), a wirelessmodem, a wireless communication device, a handheld device, a subscriberunit, a laptop computer, etc.

At transmitter 118, a transmit (TX) data processor 120 receives andprocesses (e.g., formats, encodes, and interleaves) data and providescoded data. A modulator 130 performs modulation on the coded data andprovides a modulated signal. Modulator 130 may perform Gaussian minimumshift keying (GMSK) for GSM, 8-ary phase shift keying (8-PSK) forEnhanced Data rates for Global Evolution (EDGE), etc. GMSK is acontinuous phase modulation protocol whereas 8-PSK is a digitalmodulation protocol. A transmitter unit (TMTR) 132 conditions (e.g.,filters, amplifies, and upconverts) the modulated signal and generatesan RF modulated signal, which is transmitted via an antenna 134.

At receiver 150, an antenna 152 receives RF modulated signals fromtransmitter 110 and other transmitters. Antenna 152 provides a receivedRF signal to a receiver unit (RCVR) 154. Receiver unit 154 conditions(e.g., filters, amplifies, and downconverts) the received RF signal,digitizes the conditioned signal, and provides samples. A demodulator160 processes the samples as described below and provides demodulateddata. A receive (RX) data processor 170 processes (e.g., deinterleavesand decodes) the demodulated data and provides decoded data. In general,the processing by demodulator 160 and RX data processor 170 iscomplementary to the processing by modulator 130 and TX data processor120, respectively, at transmitter 110.

Controllers/processors 140 and 180 direct operation at transmitter 118and receiver 150, respectively. Memories 142 and 182 store program codesin the form of computer software and data used by transmitter 118 andreceiver 150, respectively.

FIG. 2 shows a block diagram of a design of receiver unit 154 anddemodulator 160 at receiver 150 in FIG. 1. Within receiver unit 154, areceive chain 440 processes the received RF signal and provides I and Qbaseband signals, which are denoted as I_(bb) and Q_(bb). Receive chain440 may perform low noise amplification, analog filtering, quadraturedownconversion, etc. An analog-to-digital converter (ADC) 442digitalizes the I and Q baseband signals at a sampling rate of f_(adc)and provides I and Q samples, which are denoted as I_(adc) and Q_(adc).In general, the ADC sampling rate f_(adc) may be related to the symbolrate f_(sym) by any integer or non-integer factor.

Within demodulator 160, a pre-processor 420 performs pre-processing onthe I and Q samples from ADC 442. For example, pre-processor 420 mayremove direct current (DC) offset, remove frequency offset, etc. Aninput filter 422 filters the samples from pre-processor 420 based on aparticular frequency response and provides input I and Q samples, whichare denoted as I_(in) and Q_(in). Filter 422 may filter the I and Qsamples to suppress images resulting from the sampling by ADC 442 aswell as jammers. Filter 422 may also perform sample rate conversion,e.g., from 24× oversampling down to 2× oversampling. A data filter 424filters the input I and Q samples from input filter 422 based on anotherfrequency response and provides output I and Q samples, which aredenoted as I_(out) and Q_(out). Filters 422 and 424 may be implementedwith finite impulse response (FIR) filters, infinite impulse response(IIR) filters, or filters of other types. The frequency responses offilters 422 and 424 may be selected to achieve good performance. In onedesign, the frequency response of filter 422 is fixed, and the frequencyresponse of filter 424 is configurable.

An adjacent channel interference (ACI) detector 430 receives the input Iand Q samples from filter 422, detects for ACI in the received RFsignal, and provides an ACI indicator to filter 424. The ACI indicatormay indicates whether or not ACI is present and, if present, whether theACI is due to the higher RF channel centered at +200 KHz and/or thelower RF channel centered at −200 KHz. The frequency response of filter424 may be adjusted based on the ACI indicator, as described below, toachieve good performance.

An equalizer/detector 426 receives the output I and Q samples fromfilter 424 and performs equalization, matched filtering, detection,and/or other processing on these samples. For example,equalizer/detector 426 may implement a maximum likelihood sequenceestimator (MLSE) that determines a sequence of symbols that is mostlikely to have been transmitted given a sequence of I and Q samples anda channel estimate.

The Global System for Mobile Communications (GSM) is a widespreadstandard in cellular, wireless communication. GSM employs a combinationof Time Division Multiple Access (TDMA) and Frequency Division MultipleAccess (FDMA) for the purpose of sharing the spectrum resource. GSMnetworks typically operate in a number of frequency bands. For example,for uplink communication, GSM-900 commonly uses a radio spectrum in the890-915 MHz bands (Mobile Station to Base Transceiver Station). Fordownlink communication, GSM 900 uses 935-960 MHz bands (base station tomobile station). Furthermore, each frequency band is divided into 200kHz carrier frequencies providing 124 RF channels spaced at 200 kHz.GSM-1900 uses the 1850-1910 MHz bands for the uplink and 1930-1990 MHzbands for the downlink. Like GSM 900, FDMA divides the GSM-1900 spectrumfor both uplink and downlink into 200 kHz-wide carrier frequencies.Similarly, GSM-850 uses the 824-849 MHz bands for the uplink and 869-894MHz bands for the downlink, while GSM-1800 uses the 1710-1785 MHz bandsfor the uplink and 1805-1880 MHz bands for the downlink.

Each channel in GSM is identified by a specific absolute radio frequencychannel identified by an Absolute Radio Frequency Channel Number orARFCN. For example, ARFCN 1-124 are assigned to the channels of GSM 900,while ARFCN 512-810 are assigned to the channels of GSM 1900. Similarly,ARFCN 128-251 are assigned to the channels of GSM 850, while ARFCN512-885 are assigned to the channels of GSM 1800. Also, each basestation is assigned one or more carrier frequencies. Each carrierfrequency is divided into eight time slots (which are labeled as timeslots 0 through 7) using TDMA such that eight consecutive time slotsform one TDMA frame with a duration of 4.615 ms. A physical channeloccupies one time slot within a TDMA frame. Each active wirelessdevice/user is assigned one or more time slot indices for the durationof a call. User-specific data for each wireless device is sent in thetime slot(s) assigned to that wireless device and in TDMA frames usedfor the traffic channels.

Each time slot within a frame is used for transmitting a “burst” of datain GSM. Sometimes the terms time slot and burst may be usedinterchangeably. Each burst includes two tail fields, two data fields, atraining sequence (or midamble) field, and a guard period (GP). Thenumber of symbols in each field is shown inside the parentheses. A burstincludes 148 symbols for the tail, data, and midamble fields. No symbolsare sent in the guard period. TDMA frames of a particular carrierfrequency are numbered and formed in groups of 26 or 51 TDMA framescalled multi-frames.

FIG. 3 shows example frame and burst formats in GSM. The timeline fortransmission is divided into multiframes. For traffic channels used tosend user-specific data, each multiframe in this example includes 26TDMA frames, which are labeled as TDMA frames 0 through 25. The trafficchannels are sent in TDMA frames 0 through 11 and TDMA frames 13 through24 of each multiframe. A control channel is sent in TDMA frame 12. Nodata is sent in idle TDMA frame 25, which is used by the wirelessdevices to make measurements for neighbor base stations.

FIG. 4 shows an example spectrum in a GSM system. In this example, fiveRF modulated signals are transmitted on five RF channels that are spacedapart by 200 KHz. The RF channel of interest is shown with a centerfrequency of 0 Hz. The two adjacent RF channels have center frequenciesthat are +200 KHz and −200 KHz from the center frequency of the desiredRF channel. The next two nearest RF channels (which are referred to asblockers or non-adjacent RF channels) have center frequencies that are+400 KHz and −400 KHz from the center frequency of the desired RFchannel. There may be other RF channels in the spectrum, which are notshown in FIG. 3 for simplicity. In GSM, an RF modulated signal isgenerated with a symbol rate of f_(sym)=13000/40=270.8 kilosymbols/second (Ksps) and has a −3 dB bandwidth of up to ±135 KHz. TheRF modulated signals on adjacent RF channels may thus overlap oneanother at the edges, as shown in FIG. 4.

One or more modulation schemes are used in GSM to communicateinformation such as voice, data, and/or control information. Examples ofthe modulation schemes may include GMSK (Gaussian Minimum Shift Keying),M-ary QAM (Quadrature Amplitude Modulation) or M-ary PSK (Phase ShiftKeying), where M=2^(n), with n being the number of bits encoded within asymbol period for a specified modulation scheme. GMSK, is a constantenvelope binary modulation scheme allowing raw transmission at a maximumrate of 270.83 kilobits per second (Kbps).

GSM is efficient for standard voice services. However, high-fidelityaudio and data services desire higher data throughput rates due toincreased demand on capacity to transfer both voice and data services Toincrease capacity, the General Packet Radio Service (GPRS), EDGE(Enhanced Data rates for GSM Evolution) and UMTS (Universal MobileTelecommunications System) standards have been adopted in GSM systems.

General Packet Radio Service (GPRS) is a non-voice service. It allowsinformation to be sent and received across a mobile telephone network.It supplements Circuit Switched Data (CSD) and Short Message Service(SMS). GPRS employs the same modulation schemes as GSM. GPRS allows foran entire frame (all eight time slots) to be used by a single mobilestation at the same time. Thus, higher data throughput rates areachievable.

The EDGE standard uses both the GMSK modulation and 8-PSK modulation.Also, the modulation type can be changed from burst to burst. 8-PSKmodulation in EDGE is a linear, 8-level phase modulation with 3π/8rotation, while GMSK is a non-linear, Gaussian-pulse-shaped frequencymodulation. However, the specific GMSK modulation used in GSM can beapproximated with a linear modulation (i.e., 2-level phase modulationwith a π/2 rotation). The symbol pulse of the approximated GMSK and thesymbol pulse of 8-PSK are identical.

In GSM/EDGE, frequency bursts (FB) are sent regularly by the BaseStation (BS) to allow Mobile Stations (MS) to synchronize their LocalOscillator (LO) to the Base Station LO, using frequency offsetestimation and correction. These bursts comprise a single tone, whichcorresponds to an all “0” payload and training sequence. The all zeropayload of the frequency burst is a constant frequency signal, or asingle tone burst. When in power-on or camp-on mode or when firstaccessing the network, the remote station hunts continuously for afrequency burst from a list of carriers. Upon detecting a frequencyburst, the MS will estimate the frequency offset relative to its nominalfrequency, which is 67.7 KHz from the carrier. The MS LO will becorrected using this estimated frequency offset. In power-on mode, thefrequency offset can be as much as +/−19 KHz. The MS will periodicallywake up to monitor the frequency burst to maintain its synchronizationin standby mode. In the standby mode, the frequency offset is within ±2KHz.

Modern mobile cellular telephones are able to provide conventional voicecalls and data calls. The demand for both types of calls continues toincrease, placing increasing demands on network capacity. Networkoperators address this demand by increasing their capacity. This isachieved for example by dividing or adding cells and hence adding morebase stations, which increases hardware costs. It is desirable toincrease network capacity without unduly increasing hardware costs, inparticular to cope with unusually large peak demand during major eventssuch as an international football match or a major festival, in whichmany users or subscribers who are located within a small area wish toaccess the network at one time. When a first remote station is allocateda channel for communication (a channel comprising a channel frequencyand a time slot), a second remote station can only use the allocatedchannel after the first remote station has finished using the channel.Maximum cell capacity is reached when all the allocated channelfrequencies are used in the cell and all available time slots are eitherin use or allocated. This means that any additional remote station userwill not be able to get service. In reality, another capacity limitexists due to co-channel interferences (CCI) and adjacent channelinterferences (ACI) introduced by high frequency re-use pattern and highcapacity loading (such as 80% of timeslots and channel frequencies).

Network operators have addressed this problem in a number of ways, allof which require added resources and added cost. For example, oneapproach is to divide cells into sectors by using sectored, ordirectional, antenna arrays. Each sector can provide communications fora subset of remote stations within the cell and the interference betweenremote stations in different sectors is less than if the cell were notdivided into sectors and all the remote stations were in the same cell.Another approach is to divide cells into smaller cells, each new smallercell having a base station. Both these approaches are expensive toimplement due to added network equipment. In addition, adding cells ordividing cells into several smaller cells can result in remote stationswithin one cell experiencing more CCI and ACI interference fromneighboring cells because the distance between cells is reduced.

SUMMARY OF THE INVENTION

In a first embodiment, the present patent application comprises means,steps and instructions for combining two signals, comprising modulatingthe signals, multiplying the signals by a gain, phase shifting thesignals, adding the signals together, and transmitting the addedsignals. In another embodiment, the present patent application furthercomprises means, steps and instructions for mapping the signals to I andQ axis; and filtering the signals, wherein I and Q signals are phaseshifted on every symbol by π/2.

In another embodiment, the present patent application comprises anapparatus to combine two signals, comprising at least one basebandmodulator, at least one amplifier, whereby the signals are multiplied bya gain; and at least one combiner operably connected to the at least oneamplifier, whereby the signals are combined.

In another embodiment; the apparatus further comprises a phase shifteroperably connected to the at least one baseband modulator to provide aπ/2 phase shift between the two signals prior to combining the signals,and the at least one baseband modulator comprises a BPSK basebandmodulator on an I axis and a BPSK baseband modulator on a Q axis.

In another embodiment, the present patent application comprises a basestation comprising a controller processor, an antenna, a duplexer switchoperably connected to the base station antenna, a receiver front endoperably connected to the duplexer switch, a receiver demodulatoroperably connected to the receiver front end, a channel decoder andde-interleaver operably connected to the receiver demodulator and thecontroller processor, a base station controller interface operablyconnected to the controller processor, a coder and interleaver operablyconnected to the controller processor, a transmitter modulator operablyconnected to the coder and interleaver, a transmitter front end moduleoperably connected between said transmitter modulator and the duplexerswitch, a data bus operably connected between said controller processorand said channel decoder and de-interleaver, said receiver demodulator,said receiver front end, said transmitter modulator and said transmitterfront end; and an apparatus to combine two signals, comprising at leastone baseband modulator, at least one amplifier operably connected to theat least one baseband modulator, whereby the signals are multiplied by again; and at least one combiner operably connected to the at least oneamplifier, whereby the signals are combined, and a phase shifteroperably connected to the at least one baseband modulator. In anotherembodiment, the base station further comprises a phase shifter operablyconnected to the at least one baseband modulator to provide a π/2 phaseshift between the two signals and the at least one baseband modulatorcomprises a BPSK baseband modulator on an I axis and a BPSK basebandmodulator on a Q axis.

Further scope of the applicability of the present method and apparatuswill become apparent from the following detailed description, claims,and drawings. However, it should be understood that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects and advantages of the invention will become moreapparent from the detailed description set forth below when taken inconjunction with the accompanying drawings.

FIG. 1 shows a block diagram of a transmitter and a receiver.

FIG. 2 shows a block diagram of a receiver unit and a demodulator.

FIG. 3 shows example frame and burst formats in GSM.

FIG. 4 shows an example spectrum in a GSM system.

FIG. 5 is a simplified representation of a cellular communicationssystem;

FIG. 6 shows an arrangement of cells which are part of a cellularsystem;

FIG. 7 shows an example arrangement of time slots for a time divisionmultiple access (TDMA) communications system;

FIG. 8A shows an apparatus for operating in a multiple accesscommunication system to produce first and second signals sharing asingle channel;

FIG. 8B shows an apparatus for operating in a multiple accesscommunication system to produce first and second signals sharing asingle channel and using a combiner to combine first and secondmodulated signals;

FIG. 9 of the accompanying drawings is a flowchart disclosing a methodfor using the apparatus shown in any of FIG. 8, 10 or 11 of theaccompanying drawings;

FIG. 10A shows an example embodiment wherein the method described byFIG. 9 would reside in the base station controller;

FIG. 10B is a flowchart disclosing the steps executed by the basestation controller of FIG. 10A;

FIG. 11 shows a base station in aspects illustrating the flow of signalsin a base station;

FIG. 12 shows example arrangements for data storage within a memorysubsystem which might reside within a base station controller (BSC) of acellular communication system.

FIG. 13 shows an example receiver architecture for a remote stationhaving the DARP feature of the present method and apparatus;

FIG. 14 shows part of a GSM system adapted to assign the same channel totwo remote stations;

FIG. 15 of the accompanying drawings discloses a first example of anapparatus for combining and transmitting two signals with differentamplitudes;

FIG. 16 of the accompanying drawings discloses a second example of anapparatus for combining and transmitting two signals with differentamplitudes;

FIG. 17 of the accompanying drawings discloses a third example of anapparatus for combining and transmitting two signals with differentamplitudes;

FIG. 18 of the accompanying drawings discloses a fourth example of anapparatus for combining and transmitting two signals with differentamplitudes;

FIG. 19 illustrates an alternative approach or example for combining twosignals by mapping both users' data onto the I and Q axis respectivelyof a QPSK constellation;

FIG. 20 is a QPSK constellation diagram;

FIG. 21A of the accompanying drawings shows a flowchart disclosing thesteps for combining and transmitting two signals with differentamplitudes;

FIG. 21B of the accompanying drawings shows a flowchart disclosing thesteps for combining signals by mapping both users the I and Q axisrespectively of a QPSK constellation;

FIG. 21C of the accompanying drawings shows a flowchart disclosing thesteps for combining and transmitting two signals with differentamplitudes;

FIG. 22 is a flowchart comprising disclosing the steps taken by whenadapting a non-MUROS base station to identify an enabledMUROS-capability in a remote base station; and

FIG. 23 shows a base station with software stored in memory which mayexecute the method disclosed in FIGS. 21A, 21B, 21C and 22.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention can be practiced. The term “exemplary”used throughout this description means “serving as an example, instance,or illustration,” and should not necessarily be construed as preferredor advantageous over other embodiments. The detailed descriptionincludes specific details for the purpose of providing a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout these specific details. In some instances, well known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the present invention.

Interference due to other users limits the performance of wirelessnetworks. This interference can take the form of either interferencefrom neighboring cells on the same frequency, known as CCI, discussedabove, or neighboring frequencies on the same cell, known as ACI, alsodiscussed above.

Single-antenna interference cancellation (SAIC) is used to reduceCo-Channel Interference (CCI), The 3G Partnership Project (3GPP) hasstandardized SAIC performance. SAIC is a method used to combatinterference. The 3GPP adopted downlink advanced receiver performance(DARP) to describe the receiver that applies SAIC.

DARP increases network capacity by employing lower reuse factors.Furthermore, it suppresses interference at the same time. DARP operatesat the baseband part of a receiver of a remote station. It suppressesadjacent-channel and co-channel interference that differ from generalnoise. DARP is available in previously defined GSM standards (sinceRel-6 in 2004) as a release-independent feature, and is an integral partof Rel-6 and later specs. The following is a description of two DARPmethods. The first is the joint detection/demodulation (JD) method. JDuses knowledge of the GSM signal structure in adjacent cells insynchronous mobile networks to demodulate one of several interferencesignals in addition to the desired signal. JD's ability to retrieveinterference signals allows the suppression of specific adjacent-channelinterferers. In addition to demodulating GMSK signals, JD also can beused to demodulate EDGE signals. Blind interferer cancellation (BIC) isanother method used in DARP to demodulate the GMSK signal. With BIC, thereceiver has no knowledge of the structure of any interfering signalsthat may be received at the same time that the desired signal isreceived. Since the receiver is effectively “blind” to anyadjacent-channel interferers, the method attempts to suppress theinterfering component as a whole. The GMSK signal is demodulated fromthe wanted carrier by the BIC method. BIC is most effective when usedfor GMSK-modulated speech and data services and can be used inasynchronous networks.

A DARP capable remote station equalizer/detector 426 of the presentmethod and apparatus also performs CCI cancellation prior toequalization, detection, etc. Equalizer/detector 426 in FIG. 2 providesdemodulated data. CCI cancellation normally is available on a BS 110,111, 114. Also, remote stations 123-127 may or may not be DARP capable.The network may determine whether a remote station is DARP capable ornot at the resource assignment stage, a starting point of a call, orduring the power-on stage for a GSM remote station (e.g. mobilestation).

It is desirable to increase the number of active connections to remotestations that can be handled by a base station. FIG. 5 of theaccompanying drawings shows a simplified representation of a cellularcommunications system 100. The system comprises base stations 110, 111and 114 and remote stations 123, 124, 125, 126 and 127. Base stationcontrollers 141 to 144 act to route signals to and from the differentremote stations 123-127, under the control of mobile switching centres151, 152. The mobile switching centres 151, 152 are connected to apublic switched telephone network (PSTN) 162. Although remote stations123-127 are commonly handheld mobile devices, many fixed wirelessdevices and wireless devices capable of handling data also fall underthe general title of remote station 123-127.

Signals carrying, for example, voice data are transferred between eachof the remote stations 123-127 and other remote stations 123-127 bymeans of the base station controllers 141-144 under the control of themobile switching centres 151, 152. Alternatively, signals carrying, forexample, voice data are transferred between each of the remote stations123-127 and other communications equipment of other communicationsnetworks via the public switched telephone network 162. The publicswitched telephone network 162 allows calls to be routed between themobile cellular system 100 and other communication systems. Such othersystems include other mobile cellular communications systems 100 ofdifferent types and conforming to different standards.

Each of remote stations 123-127 can be serviced by any one of a numberof base stations 110, 111, 114. A remote station 124 receives both asignal transmitted by the serving base station 114 and signalstransmitted by nearby non-serving base stations 110, 111 and intended toserve other remote stations 125.

The strengths of the different signals from base stations 110, 111, 114are periodically measured by the remote station 124 and reported to BSC144, 114, etc. If the signal from a nearby base station 110, 111 becomesstronger than that of the serving base station 114, then the mobileswitching centre 152 acts to make the nearby base station 110 become theserving base station and acts to make the serving base station 114become a non-serving base station and handovers the signal to the nearbybase station 110. Handover refers to the method of transferring a datasession or an ongoing call from one channel connected to the corenetwork to another.

In cellular mobile communications systems, radio resources are dividedinto a number of channels. Each active connection (for example a voicecall) is allocated a particular channel having a particular channelfrequency for the downlink signal (transmitted by the base station 110,111, 114 to a remote station 123-127 and received by the remote station123-127) and a channel having a particular channel frequency for theuplink signal (transmitted by the remote station 123-127 to the basestation 110, 111, 114 and received by the base station 110, 111, 114).The frequencies for downlink and uplink signals are often different, toallow simultaneous transmission and reception and to reduce interferencebetween transmitted signals and the received signals at the remotestation or 123-127 at the base station 110, 111, 114.

A method for cellular systems to provide access to many users isfrequency reuse. FIG. 6 of the accompanying drawings shows anarrangement of cells in a cellular communications system that usesfrequency reuse. This particular example has a reuse factor of 4:12,which represents 4 sites and 12 frequencies. That means that the 12frequencies available for use by a base station are allocated to thebase stations of four sites labeled A-D, each site having one basestation 110, 111, 114. Each site is divided into three sectors (nowusually called cells). Stated another way, one frequency is allocated toeach of the three cells of each of 4 sites so that all of the 12 cellshave different frequencies. The frequency reuse pattern repeats itselfas shown in the figure. Base station 110 belongs to cell A, base station114 belongs to cell B, base station 111 belongs to cell C and so on.Base station 110 has a service area 220 that overlaps with adjacentservice areas 230 and 240 of adjacent base stations 111 and 114respectively. Remote stations 124, 125 are free to roam between theservice areas. As discussed above, to reduce interference of signalsbetween cells, each site is allocated a set of channel frequencies whichis different to the set of channel frequencies allocated to each of itsneighboring sites. However, two sites that are non-adjacent may use thesame set of frequencies. Base station 110 could use for examplefrequency allocation set A comprising frequencies f1, f2 and f3 forcommunicating with remote stations 125 in its service area 220.Similarly, base station 114 could use for example frequency allocationset B comprising frequencies f4, f5 and f6, to communicate with remotestations 124 in its service area 240, and so on. The area defined bybold border 250 contains one four-site repeat pattern. The repeatpattern repeats in a regular arrangement for the geographical areaserviced by the communications system 100. It may be appreciated thatalthough the present example repeats itself after 4 sites, a repeatpattern may have a number of sites other than four and a total number offrequencies other than 12.

TDMA is a multiple access technique directed to providing increasedcapacity. Using TDMA, each carrier frequency is segmented into timeintervals called frames. Each frame is further partitioned intoassignable user time slots. In GSM, the frame is partitioned into eighttime slots. Thus, eight consecutive time slots form one TDMA frame witha duration of 4.615 ms.

A physical channel occupies one time slot within each frame on aparticular frequency. The TDMA frames of a particular carrier frequencyare numbered, each user being assigned one or more time slots withineach frame. Furthermore, the frame structure repeats, so that a fixedTDMA assignment constitutes one or more slots that periodically appearduring each time frame. Thus, each base station can communicate with aplurality of remote stations 123-127 using different assigned time slotswithin a single channel frequency. As stated above, the time slotsrepeat periodically. For example, a first user may transmit on the1^(st) slot of every frame of frequency f1, while a second user maytransmit on the 2^(nd) slot of every frame of frequency 12. During eachdownlink time slot, the remote station 123-127 is given access toreceive a signal transmitted by the base station 110, 111, 114 andduring each uplink time slot the base station 110, 111, 114 is givenaccess to receive a signal transmitted by the remote station 123-127.The channel for communication to a remote station 123-127 thus comprisesboth a frequency and a time slot, for a GSM system. Equally, the channelfor communication to a base station 110, 111, 114 comprises both afrequency and a time slot.

FIG. 7 shows an example arrangement of time slots for a time divisionmultiple access (TDMA) communications system. A base station 114transmits data signals in a sequence of numbered time slots 30, eachsignal being for only one of a set of remote stations 123-127 and eachsignal being received at the antenna of all remote stations 123-127within range of the transmitted signals. The base station 114 transmitsall the signals using slots on an allocated channel frequency. Forexample, a first remote station 124 might be allocated a first time slot3 and a second remote station 126 might be allocated a second time slot5. The base station 114 transmits, in this example, a signal for thefirst remote station 124 during time slot 3 of the sequence of timeslots 30, and transmits a signal for the second remote station 126during time slot 5 of the sequence of time slots 30. The first andsecond remote stations 124, 126 are active during their respective timeslots 3 and 5 of time slot sequence 30, to receive the signals from thebase station 114. The remote stations 124, 126 transmit signals to thebase station 114 during corresponding time slots 3 and 5 of time slotsequence 31 on the uplink. It can be seen that the time slots for thebase station 114 to transmit (and the remote stations 124, 126 toreceive) 30 are offset in time with respect to the time slots for theremote stations 124, 126 to transmit (and the base station 114 toreceive) 31.

This offsetting in time of transmit and receive time slots is known astime division duplexing (TDD), which among other things, allows transmitand receive operations to occur at different instances of time.

Voice and data signals are not the only signals to be transmittedbetween the base station 110, 111, 114 and the remote station 123-127. Acontrol channel is used to transmit data that controls various aspectsof the communication between the base station 110, 111, 114 and theremote station 123-127. Among other things, the base station 110, 111,114 uses the control channel to send to the remote station 123-127 asequence code, or training sequence code (TSC) which indicates which ofa set of sequences the base station 110, 111, 114 will use to transmitthe signal to the remote station 123-127. In GSM, a 26-bit trainingsequence is used for equalization. This is a known sequence which istransmitted in a signal in the middle of every time slot burst.

The sequences are used by the remote station 123-127 to compensate forchannel degradations which vary quickly with time; to reduceinterference from other sectors or cells; and to synchronize the remotestation's 123-127 receiver to the received signal. These functions areperformed by an equalizer which is part of the remote station's 123-127receiver. An equalizer 426 determines how the known transmitted trainingsequence signal is modified by multipath fading. Equalization may usethis information to extract the desired signal from the unwantedreflections by constructing an inverse filter to extract the rest of thedesired signal. Different sequences (and associated sequence codes) aretransmitted by different base stations 110, 111, 114 in order to reduceinterference between sequences transmitted by base stations 110, 111,114 that are close to each other.

As stated above, with DARP the remote station 123-127 of the presentmethod and apparatus is able to use the sequence to distinguish thesignal transmitted to it by the base station 110, 111, 114 serving theremote station 123-127 from other unwanted signals transmitted bynon-serving base stations 110, 111, 114 of other cells. This holds trueso long as the received amplitudes or power levels of the unwantedsignals are below a threshold relative to the amplitude of the wantedsignal. The unwanted signals can cause interference to the wanted signalif they have amplitudes above this threshold. In addition, the thresholdcan vary according to the capability of the remote station's 123-127receiver. The interfering signal and the desired (or wanted) signal canarrive at the remote station's 123-127 receiver contemporaneously if,for example, the signals from the serving and non-serving base stations110, 111, 114 share the same time slot for transmitting.

Referring again to FIG. 5, at remote station 124, transmissions frombase station 110 for remote station 125 can interfere with transmissionsfrom base station 114 for remote station 124 (the path of theinterfering signal shown by dashed arrow 170). Similarly, at remotestation 125 transmissions from base station 114 for remote station 124can interfere with transmissions from base station 110 for remotestation 125 (the path of the interfering signal shown by dotted arrow182).

TABLE 1

Table 1 shows example values of parameters for signals transmitted bythe two base stations 110 and 114 illustrated in FIG. 6. The informationin rows 3 and 4 of Table 1 show that for remote station 124 both awanted signal from a first base station 114 and an unwanted interferersignal from a second base station 110 and intended for remote station125 are received and the two received signals have the same channel andsimilar power levels (−82 dBm and −81 dBm respectively). Similarly, theinformation in rows 6 and 7 show that for remote station 125 both awanted signal from the second base station 110 and an unwantedinterferer signal from the first base station 114 and intended forremote station 124 are received and the two received signals have thesame channel and similar power levels (−80 dBm and −79 dBmrespectively).

Each remote station 124, 125 thus receives both a wanted signal and anunwanted interferer signal that have similar power levels from differentbase stations 114, 110, on the same channel (i.e. contemporaneously).Because the two signals arrive on the same channel and similar powerlevels, they interfere with each other. This may cause errors indemodulation and decoding of the wanted signal. This interference isco-channel interference discussed above.

The co-channel interference may be mitigated to a greater extent thanpreviously possible, by the use of DARP enabled remote stations 123-127,base stations 110, 111, 114 and base station controllers 151, 152. Whilebase stations 110, 111, 114 may be capable of simultaneously receivingand demodulating two co-channel signals having similar power levels,DARP allows remote stations 123-127 to have, by means of DARP, similarcapability. This DARP capability may be implemented by means of SAIC orby means of a method known as dual antenna interference cancellation(DAIC).

The receiver of a DARP-capable remote station 123-127 may demodulate awanted signal while rejecting an unwanted co-channel signal even whenthe amplitude of the received unwanted co-channel signal is similar orhigher than the amplitude of the wanted signal. The DARP feature worksbetter when the amplitudes of the received co-channel signals aresimilar. This situation would typically occur in existing systems suchas GSM not yet employing the present method and apparatus, when each oftwo remote stations 123-127, each communicating with a different basestation 110, 111, 114, is near a cell boundary, where the path lossesfrom each base station 110, 111, 114 to each remote station 123-127 aresimilar.

A remote station 123-127 that is not DARP-capable, by contrast, may onlydemodulate the wanted signal if the unwanted co-channel interferersignal has an amplitude, or power level, lower than the amplitude of thewanted signal. In one example, it may be lower by at least 8 dB. TheDARP-capable remote station 123-127 can therefore tolerate a muchhigher-amplitude co-channel signal relative to the wanted signal, thancan the remote station 123-127 not having DARP capability.

The co-channel interference (CCI) ratio is the ratio between the powerlevels, or amplitudes, of the wanted and unwanted signals expressed indB. In one example, the co-channel interference ratio could be, forexample, −6 dB (whereby the power level of the wanted signal is 6 dBlower than the power level of the co-channel interferer (or unwanted)signal). In another example, the ratio may be +6 dB (whereby the powerlevel of the wanted signal is 6 dB higher than the power level of theco-channel interferer (or unwanted) signal). For those remote stations123-127 of the present method and apparatus with good DARP performance,the amplitude of the interferer signal can be as much as 10 dB higherthan the amplitude of the wanted signal, and the remote stations 123-127may still process the wanted signal. If the amplitude of the interferersignal is 10 dB higher than the amplitude of the wanted signal, theco-channel interference ratio is −10 dB.

DARP capability, as described above, improves a remote station's 123-127reception of signals in the presence of ACI or CCI. A new user, withDARP capability, will better reject the interference coming from anexisting user. The existing user, also with DARP capability, would dothe same and not be impacted by the new user. In one example, DARP workswell with CCI in the range of 0 dB (same level of co-channelinterference for the signals) to −6 dB (co-channel is 6 dB stronger thanthe desired or wanted signal). Thus, two users using the same ARFCN andsame timeslot, but assigned different TSCs, will get good service.

The DARP feature allows two remote stations 124 and 125, if they bothhave the DARP feature enabled, to each receive wanted signals from twobase stations 110 and 114, the wanted signals having similar powerlevels, and each remote station 124, 125 to demodulate its wantedsignal. Thus, the DARP enabled remote stations 124, 125 are both able touse the same channel simultaneously for data or voice.

The feature described above of using a single channel to support twosimultaneous calls from two base stations 110, 111, 114 to two remotestations 123-127 is somewhat limited in its application in the priorart. To use the feature, the two remote stations 124, 125 are withinrange of the two base stations 114, 110 and are each receiving the twosignals at similar power levels. For this condition, typically the tworemote stations 124, 125 would be near the cell boundary, as mentionedabove.

The present method and apparatus allows the supporting of two or moresimultaneous calls on the same channel (consisting of a time slot on acarrier frequency), each call comprising communication between a singlebase station 110, 111, 114 and one of a plurality of remote stations123-127 by means of a signal transmitted by the base station 110, 111,114 and a signal transmitted by the remote station 123-127. The presentmethod and apparatus provides a new and inventive application for DARP.As stated above, with DARP, two signals on the same time slot on thesame carrier frequency may be distinguished by using different trainingsequences at higher levels of interference than before DARP. Since thesignal from the BS 110, 111, 114 not being used acts as interference,DARP filters/suppresses out the unwanted signal (signal from the BS 110,111, 114 not being used) by use of the training sequences.

The present method and apparatus allows the use of two or more trainingsequences in the same cell. In the prior art, one of the trainingsequences, the one not assigned to the base station 110, 111, 114, willonly act as interference as it also does in Multi-User on One Slot(MUROS) for at least one mobile station's 123-127 receiver. However, akey difference is that the unwanted signal for that mobile station123-127 is wanted by another mobile station 123-127 in the same cell. Inlegacy systems, the unwanted signal is for a mobile station 123-127 inanother cell. According to the present method and apparatus, bothtraining sequence signals may be used in the same time slot on the samecarrier frequency in the same cell by the same base station 110, 111,114. Since two training sequences can be used in a cell, twice as manycommunication channels may be used in the cell. By taking a trainingsequence which would normally be interference from another(non-neighboring) cell or sector and allowing a base station 110, 111,114 to use it in addition to its already-used training sequence for thesame time slot, the number of communication channels is doubled. Ifthree training sequences are used in the same time slot in this way, thenumber of communication channels is tripled.

DARP, when used along with the present method and apparatus, thereforeenables a GSM network to use a co-channel already in use (i.e., theARFCN that is already in use) to serve additional users. In one example,each ARFCN can be used for two users for full-rate (FR) speech and 4 forhalf-rate (HR) speech. It is also possible to serve the third or evenfourth user if the remote stations 123-127 have excellent DARPperformance. In order to serve additional users using the same AFRCN onthe same timeslot, the network transmits the additional users' RF signalon the same carrier, using a different phase shift, and assigns the sametraffic channel (the same ARFCN and timeslot that is in use) to theadditional user using a different TSC. The bursts are modulated with thetraining sequence corresponding to the TSC accordingly. A DARP capableremote station 123-127 may detect the wanted or desired signal. It ispossible to add the third and fourth users in the same way as the firstand second users were.

FIG. 8A of the accompanying drawings shows an apparatus for operating ina multiple access communication system to produce first and secondsignals sharing a single channel. A first data source 401 and a seconddata source 402 (for a first and a second remote station 123-127)produce first data 424 and second data 425 for transmission. A sequencegenerator 403 generates a first sequence 404 and a second sequence 405.A first combiner 406 combines the first sequence 404 with the first 424data to produce first combined data 408. A second combiner 407 combinesthe second sequence 405 with the second data 425 to produce secondcombined data 409.

The first and second combined data 408, 409 are input to a transmittermodulator 410 for modulating both the first and the second combined data408, 409 using a first carrier frequency 411 and a first time slot 412.In this example, the carrier frequency may generated by an oscillator421. The transmitter modulator outputs a first modulated signal 413 anda second modulated signal 414 to a RF front end 415. The RF front endprocesses the first and second modulated signals 413, 414 byupconverting them from baseband to an RF (radio frequency) frequency.The upconverted signals are sent to antennas 416 and 417 where they arerespectively transmitted.

The first and second modulated signals may be combined in a combinerprior to being transmitted. The combiner 422 may be a part of either thetransmitter modulator 410 or the RF front end 415 or a separate device.A single antenna 416 provides means for transmitting the combined firstand second signals by radiation. This is illustrated in FIG. 8B.

FIG. 9 of the accompanying drawings shows a method for using theapparatuses for operating in a multiple access communication system toproduce first and second signals sharing a single channel shown in FIGS.8A and 8B. The method includes allocating a particular channel frequencyand a particular time slot for a base station 110, 111, 114 to use totransmit to a plurality of remote stations 123-127 whereby a differenttraining sequence is assigned for each remote station 123-127. Thus inone example, this method may be executed in the base station controller151, 152. In another example, this method may be executed in a basestation 110, 111, 114.

Following the start of the method 501, a decision is made in step 502 asto whether to set up a new connection between the base station 110, 111,114 and a remote station 123-127. If the answer is NO, then the methodmoves back to the start block 501 and the steps above are repeated. Whenthe answer is YES, a new connection is set up. Then in block 503 adecision is made as to whether there is an unused channel (i.e. anunused time slot for any channel frequency). If there is an unused timeslot on a used or unused channel frequency, then a new time slot isallocated in block 504. The method then moves back to the start block501 and the steps above are repeated.

When eventually there is no longer an unused time slot (because all timeslots are used for connections), the answer to the question of block 503is NO, and the method moves to block 505. In block 505, a used time slotis selected for the new connection to share with an existing connection,according to a set of first criteria. There can be a variety ofcriteria. For example one criterion might be that a time slot may beselected if it has low traffic. Another criterion may be that the timeslot is already used by no more than one remote station 123-127. It canbe appreciated that there will be other possible criteria based on thenetwork planning methods employed, and the criteria is not limited tothose two examples.

A used time slot on a channel frequency having been selected for the newconnection to share along with an existing connection, a TSC for the newconnection is then selected in block 506 according to a set of secondcriteria. These second criteria may include some of the criteria usedfor the selection of the time slot in block 505, or other criteria. Onecriterion is that the TSC has not yet been used by the cell or sectorfor the channel comprising the used time slot. Another criterion mightbe that the TSC is not used on that channel by a nearby cell or sector.The method then moves back to the start block 501 and the steps aboveare repeated.

FIG. 10A of the accompanying drawings shows an example wherein themethod described by FIG. 9 would reside in the base station controller600. Within base station controller 600 reside controller processor 660and memory subsystem 650. The steps of the method may be stored insoftware 680 in memory 685 in memory subsystem 650, or within software680 in memory 685 residing in controller processor 660, or withinsoftware 680 memory 685 in the base station controller 600, or withinsome other digital signal processor (DSP) or in other forms of hardware.The base station controller 600 is connected to the mobile switchingcentre 610 and also to base stations 620, 630 and 640, as shown by FIG.10A.

Shown within memory subsystem 650 are parts of three tables of data 651,652, 653. Each table of data stores values of a parameter for a set ofremote stations 123, 124 indicated by the column labeled MS. Table 651stores values of training sequence code. Table 652 stores values fortime slot number TS. Table 653 stores values of channel frequency CHF.It can be appreciated that the tables of data could alternatively bearranged as a multi-dimensional single table or several tables ofdifferent dimensions to those shown in FIG. 10A.

Controller processor 660 communicates via data bus 670 with memorysubsystem 650 in order to send and receive values for parameters to/frommemory subsystem 650. Within controller processor 660 are containedfunctions that include a function 661 to generate an access grantcommand, a function 662 to send an access grant command to a basestation 620, 630, 640, a function 663 to generate a traffic assignmentmessage, and a function 664 to send a traffic assignment message to abase station 620, 630 or 640. These functions may be executed usingsoftware 680 stored in memory 685.

Within controller processor 660, or elsewhere in the base stationcontroller 600, there may also be a power control function 665 tocontrol the power level of a signal transmitted by a base station 620,630 or 640.

It can be appreciated that the functions shown as being within basestation controller 600, namely memory subsystem 650 and controllerprocessor 660 could also reside in the mobile switching centre 610.Equally some or all of the functions described as being part of basestation controller 600 could equally well reside in one or more of basestations 620, 630 or 640.

FIG. 10B is a flowchart disclosing the steps executed by the basestation controller 600. When allocating a channel to a remote station123, 124 (e.g. remote station MS 123), for example when the remotestation 123 requests service, the base station 620, 630, 640 wishing toservice the remote station 123, 124 sends a request message to the basestation controller 600 for a channel assignment. Controller processor660, upon receiving the request message at step 602 via data bus 670,determines if a new connection is required. If the answer is NO, thenthe method moves back to the start block 601 and the steps above arerepeated. When the answer is YES a new connection set up is initiated.Then in block 603 a decision is made as to whether there is an unusedchannel (i.e. an unused time slot for any channel frequency). If thereis an unused time slot on a used or unused channel frequency, then a newtime slot is allocated in block 604. The method then moves back to thestart block 601 and the steps above are repeated.

On the other hand, if the controller processor 660 determines there isnot an unused time slot on any channel frequency, it selects a used timeslot. See step 605 of FIG. 10B. The selection could be based onaccessing memory subsystem 650 or other memory 685 to obtain informationon criteria such as the current usage of time slots, and whether both oronly one of remote stations 123, 124 are DARP enabled. Controllerprocessor 660 selects a used time slot, and selects a training sequencecode for the time slot. See step 606 of FIG. 10B Since the time slot isalready used, this will be the second training sequence selected forthat time slot.

In order to apply criteria for selecting a time slot, the controllerprocessor 660 accesses memory 650 via data bus 670, or accesses othermemory 685, to obtain information, for example information about thecurrent allocation of time slots or training sequences or both, andwhether remote stations 123, 124 have DARP capability. Controllerprocessor 660 then generates a command (661 or 663) and sends thecommand (662 or 664) to the base station 620 to assign a channelfrequency, time slot and training sequence to the remote station 123.The method then moves back to the start block 601 and the steps aboveare repeated.

FIG. 11 of the accompanying drawings shows the flow of signals in a basestation 620, 920. Base station controller interface 921 communicates,via communications link 950, with a base station controller 600.Communications link 950 might be a data cable or a RF link for example.Controller processor 960 communicates with and controls, via data bus970, receiver components 922, 923 and 924, and transmitter components927, 928, and 929. Controller processor 960 communicates via data bus980 with BSC interface 921. The data bus 970 could comprise just one busor several buses and could be partly or wholly bi-directional. Databuses 970 and 980 could be the same bus.

In one example, a message requesting grant of a channel is received froma remote station 123, 124 in a coded, modulated, radiated signal at basestation antenna 925 and is input to duplexer switch 926. The signalpasses from the receive port of duplexer switch 926 to the receiverfront end 924 which conditions the signal (for example by means ofdown-converting, filtering, and amplifying). The receiver demodulator923 demodulates the conditioned signal and outputs the demodulatedsignal to channel decoder and de-interleaver 922 which decodes andde-interleaves the demodulated signal and outputs the resulting data tocontroller processor 960. Controller processor 960 derives from theresulting data the message requesting grant of a channel. Controllerprocessor 960 sends the message via base station controller interface921 to a base station controller 600. The base station controller 600then acts to grant, or not grant, a channel to the remote station 23,24, either autonomously or together with mobile switching centre 610.

Base station controller 600 generates and sends access grant commands,and other digital communication signals or traffic for remote stations123, 124, for example assignment messages, to BSC interface 921 viacommunications link 950. The signals are then sent via data bus 980 tocontroller processor 960. Controller processor 960 outputs signals forremote stations 123, 124 to coder and interleaver 929 and the coded andinterleaved signals then pass to transmitter modulator 928. It can beseen from FIG. 11 that there are several signals input to transmittermodulator 928, each signal for a remote station 123, 124. These severalsignals can be combined within transmitter modulator 928 to provide acombined modulated signal having I and Q components as shown in FIG. 11.However the combining of the several signals could alternatively beperformed post-modulation within transmitter front end module 927 and orin other stages within the transmit chain. The modulated combined signalis output from transmitter front end 927 and input to the transmit portof duplexer switch 926. The signal is then output via the common orantenna port of duplexer switch 926 to the antenna 925 for transmission.

In another example, a second message from a second remote station 123,124 requesting grant of a channel is received in a second receivedsignal at the base station antenna 925. The second received signal isprocessed as described above and the request for grant of a channel issent in the processed second received signal to the base stationcontroller 600.

The base station controller 600 generates and sends to the base station620, 920 a second access grant message as described above, and the basestation 620, 920 transmits a signal comprising the second access grantmessage, as described above, for the remote station 123, 124.

Phase Shift

The absolute phase of the modulation for the two signals transmitted bythe base station 110, 111, 114 may not be identical. In order to serveadditional users using the same channel (co-TCH), in addition toproviding more than one TSC, the network may phase shift the symbols ofthe RF signal of the new co-channel (co-TCH) remote station 123-127 withrespect to the existing co-TCH remote station(s) 123-127. If possiblethe network may control them with evenly distributed spaced phase shift,thus improving receiver performance. For example, the phase shift of thecarrier frequency (having a particular ARFCN) for two users would be 90degrees apart, three users 60 degrees apart. The phase shift of thecarrier (ARFCN) for four users would be 45 degree apart. As statedabove, the users will use different TSCs. Each additional MS 123-127 ofthe present method and apparatus is assigned a different TSC and usesits own TSC and the DARP feature to get its own traffic data.

Thus, for improved DARP performance, the two signals intended for thetwo different mobile stations (remote stations) 123, 124 may ideally bephase shifted by π/2 for their channel impulse response, but less thanthis will also provide adequate performance.

When the first and second remote stations 123, 124 are assigned the samechannel (i.e. same time slot on the same channel frequency), signals maypreferably be transmitted to the two remote stations 123, 124 (usingdifferent training sequences as described previously) such that themodulator 928 modulates the two signals at 90 degrees phase shift toeach other, thus further reducing interference between the signals dueto phase diversity. So, for example, the I and Q samples emerging fromthe modulator 928 could each represent one of the two signals, thesignals being separated by 90 degrees phase. The modulator 928 thusintroduces a phase difference between the signals for the two remotestations 123, 124.

In the case of several remote stations 123, 124 sharing the samechannel, multiple sets of I and Q samples can be generated withdifferent offsets. For example, if there is a third signal for a thirdremote station 123, 124 on the same channel, the modulator 928introduces phase shifts of preferably 60 degrees and 120 degrees for thesecond and third signals relative to the phase of the first signal, andthe resulting I and Q samples represent all three signals. For example,the I and Q samples could represent the vector sum of the three signals.

In this way, the transmitter modulator 928 provides means at the basestation 620, 920 for introducing a phase difference betweencontemporaneous signals using the same time slot on the same frequencyand intended for different remote stations 123, 124. Such means can beprovided in other ways. For example, separate signals can be generatedin the modulator 928 and resulting analogue signals can be combined inthe transmitter front end 927 by passing one of them through a phaseshift element and then simply summing the phase shifted and non-phaseshifted signals.

Power Control Aspects

Table 2 below shows example values of channel frequency, time slot,training sequence and received signal power level for signalstransmitted by the two base stations 110 and 114 as shown in FIG. 5 andreceived by remote stations 123 to 127.

TABLE 2

The rows 3 and 4 of Table 2, outlined by a bold rectangle, show bothremote station 123 and remote station 124 using channel frequency havingindex 32 and using time slot 3 for receiving a signal from base station114 but allocated different training sequences TSC2 and TSC3respectively. Similarly, rows 9 and 10 also show the same channelfrequency and time slot being used for two remote stations 125, 127 toreceive signals from the same base station 110. It can be seen that ineach case the remote station 125, 127 received power levels of thewanted signals are substantially different for the two remote stations125, 127. The highlighted rows 3 and 4 of Table 3 show that base station114 transmits a signal for remote station 123 and also transmits asignal for remote station 124. The received power level at remotestation 123 is −67 dBm whereas the received power level at remotestation 124 is −102 dBm. Rows 9 and 10 of Table 3 show that base station110 transmits a signal for remote station 125 and also transmits asignal for remote station 127. The received power level at remotestation 125 is −101 dBm whereas the received power level at remotestation 127 is −57 dBm. The large difference in power level, in eachcase, could be due to different distances of the remote stations 125,127 from the base station 110. Alternatively the difference in powerlevels could be due to different path losses or different amounts ofmulti-path cancellation of the signals, between the base stationtransmitting the signals and the remote station receiving the signals,for one remote station as compared to the other remote station.

Although this difference in received power level for one remote stationcompared to the other remote station is not intentional and not idealfor cell planning, it does not compromise the operation of the presentmethod and apparatus.

A remote station 123-127 having DARP capability may successfullydemodulate either one of two co-channel, contemporaneously receivedsignals, so long as the amplitudes or power levels of the two signalsare similar at the remote station's 123-127 antenna. This is achievableif the signals are both transmitted by the same base station 110, 111,114 and (could have more than one antenna, e.g., one per signal) thepower levels of the two transmitted signals are substantially the samebecause then each remote station 123-127 receives the two signals atsubstantially the same power level (say within 6 dB of each other). Thetransmitted powers are similar if either the base station 110, 111, 114is arranged to transmit the two signals at similar power levels, or thebase station 110, 111, 114 transmits both signals at a fixed powerlevel. This situation can be illustrated by further reference to Table 2and by reference Table 3.

While Table 2 shows remote stations 123, 124 receiving from base station114 signals having substantially different power levels, on closerinspection it can be seen that, as shown by rows 3 and 5 of Table 2,remote station 123 receives two signals from base station 114 at thesame power level (−67 dBm), one signal being a wanted signal intendedfor remote station 123 and the other signal being an unwanted signalwhich is intended for remote station 124. The criteria for a remotestation 123-127 to receive signals having similar power levels is thusshown as being met in this example. If mobile station 123 has a DARPreceiver, it can, in this example, therefore demodulate the wantedsignal and reject the unwanted signal.

Similarly, it can be seen by inspecting rows 4 and 6 of Table 2 (above)that remote station 124 receives two signals sharing the same channeland having the same power level (−102 dBm). Both signals are from basestation 114. One of the two signals is the wanted signal, for remotestation 124 and the other signal is the unwanted signal which isintended for use by remote station 123.

To further illustrate the above concepts, Table 3 is an altered versionof Table 2 wherein the rows of Table 2 are simply re-ordered. It can beseen that remote stations 123 and 124 each receive from one base station114 two signals, a wanted and an unwanted signal, having the samechannel and similar power levels. Also, remote station 125 receives fromtwo different base stations 110, 114 two signals, a wanted and anunwanted signal, having the same channel and similar power levels.

TABLE 3

The apparatus and method described above have been simulated and themethod has been found to work well in a GSM system. The apparatusdescribed above and shown in FIGS. 8A, 8B, 10A, 11 and 12 could be partof a base station 110, 111, 114 of a GSM system for example.

According to another aspect of the present method and apparatus it ispossible for a base station 110, 111, 114 to maintain a call with tworemote stations 123-127 using the same channel, such that a first remotestation 123-127 has a DARP-enabled receiver and a second remote station123-127 does not have a DARP-enabled receiver. The amplitudes of signalsreceived by the two remote stations 124-127 are arranged to be differentby an amount which is within a range of values, in one example it may bebetween 8 dB and 10 dB, and also arranged such that the amplitude of thesignal intended for the DARP-enabled remote station is lower than theamplitude of the signal intended for the non-DARP-enabled remote station124-127.

A MUROS or non-MUROS mobile may treat its unwanted signal asinterference. However, for MUROS, both signals may be treated as wantedsignals in a cell. An advantage with MUROS enabled networks (thenetworks including e.g., a BS 110, 111, 114 and BSC 141, 144) is thatthe BS 110, 111, 114 may use two or more training sequences per timeslotinstead of only one so that both signals may be treated as desiredsignals in the same cell. The BS 110, 111, 114 transmits the signals atsuitable amplitudes so that each remote station 123-127 of the presentmethod and apparatus receives its own signal at a high enough amplitudeand the two signals are maintained with an amplitude ratio such that thetwo signals corresponding to the two training sequences may be both bedetected. This feature may be implemented using software stored inmemory in the BS 110, 111, 114 or BSC 600. For example, MSs 123-127 areselected for pairing based on their path losses and based on existingtraffic channel availability. However, MUROS can still work if the pathlosses are very different for one remote station 123-127 than for theother remote station 123-127. This may occur when one remote station123-127 is much further away from the BS 110, 111, 114.

Regarding power control there are different possible combinations ofpairings. Both remote stations 123-127 can be DARP capable oralternatively only one can be DARP capable. In both cases, the receivedamplitudes or power levels at the mobile stations 123-127 may be within10 dB of each other. However if only one remote station 123-127 is DARPcapable, a further constraint is that the non-DARP mobile 123-127receives its wanted (or desired) first signal at a level higher than thelevel at which it receives the second signal (in one example, at least 8dB higher than the second signal). The DARP capable remote station123-127 receives its second signal at a level which is lower than thelevel of the first signal by an amount which is less than a thresholdamount (in one example, the second signal is no lower than 10 dB belowthe first signal). Hence in one example, the amplitude ratio can be 0 dBto ±10 dB for two DARP capable remote stations 123-127 or, in the caseof a non-DARP/DARP pairing of remote stations 123-127, the signal forthe non-DARP remote station 123-127 is received 8 dB to 10 dB higherthan the signal for the DARP remote station 123-127. Also, it ispreferable for the BS 110, 111, 114 to transmit the two signals so thateach remote station 123-127 receives its wanted signal above itssensitivity limit. (In one example, it is at least 6 dB above itssensitivity limit). So if one remote station 123-127 has more path loss,the BS 110, 111, 114 transmits that remote station's 123-127 signal atan amplitude high enough to ensure that the transmitted signal isreceived by the remote station 123-127 at a level above the sensitivitylimit. This sets the absolute transmitted amplitude for that signal. Thedifference in level required between that signal and the other signalthen determines the absolute amplitude of the other signal.

FIG. 12 of the accompanying drawings shows example arrangements for datastorage within a memory subsystem 650 which might reside within a basestation controller (BSC) 600 of the present method and apparatus ofcellular communication system 100. Table 1001 of FIG. 12 is a table ofvalues of channel frequencies assigned to remote stations 123-127, theremote stations 123-127 being numbered. Table 1002 is a table of valuesof time slots wherein remote station numbers 123-127 are shown againsttime slot number. It can be seen that time slot number 3 is assigned toremote stations 123, 124 and 229. Similarly table 1003 shows a table ofdata allocating training sequences (TSCs) to remote stations 123-127.

Table 1005 of FIG. 12 shows an enlarged table of data which ismulti-dimensional to include all of the parameters shown in tables 1001,1002, and 1003 just described. It will be appreciated that the portionof table 1005 shown in FIG. 12 is only a small part of the completetable that would be used. Table 1005 shows in addition the allocation offrequency allocation sets, each frequency allocation set correspondingto a set of frequencies used in a particular sector of a cell or in acell. In Table 1005, frequency allocation set f1 is assigned to allremote stations 123-127 shown in the table 1005 of FIG. 12. It will beappreciated that other portions of Table 1005, which are not shown, willshow frequency allocation sets f2, f3 etc. assigned to other remotestations 123-127. The fourth row of data shows no values but repeateddots indicating that there are many possible values not shown betweenrows 3 and 5 of the data in table 1001.

FIG. 13 of the accompanying drawings shows an example receiverarchitecture for a remote station 123-127 of the present method andapparatus having the DARP feature. In one example, the receiver isadapted to use either the single antenna interference cancellation(SAIC) equalizer 1105, or the maximum likelihood sequence estimator(MLSE) equalizer 1106. Other equalizers implementing other protocols mayalso be used. The SAIC equalizer is preferred for use when two signalshaving similar amplitudes are received. The MLSE equalizer is typicallyused when the amplitudes of the received signals are not similar, forexample when the wanted signal has an amplitude much greater than thatof an unwanted co-channel signal.

FIG. 14 of the accompanying drawings shows a simplified representationof part of a GSM system adapted to assign the same channel to two remotestations 123-127. The system comprises a base station transceiversubsystem (BTS), or base station 110, and two remote stations, mobilestations 125 and 127. The network can assign, via the base stationtransceiver subsystem 110, the same channel frequency and the same timeslot to the two remote stations 125 and 127. The network allocatesdifferent training sequences to the two remote stations 125 and 127.Remote stations 125 and 127 are both mobile stations and are bothassigned a channel frequency having ARFCN equal to 160 and a time slotwith time slot index number, TS, equal to 3. Remote station 125 isassigned training sequence having a TSC of 5 whereas remote station 127is assigned training sequence having a TSC of 0. Each remote station125, 127 will receive its own signal (shown by solid lines in thefigure) together with the signal intended for the other remote station125, 127 (shown by dotted lines in the figure). Each remote station 125,127 is able to demodulate its own signal whilst rejecting the unwantedsignal.

As described above, according to the present method and apparatus asingle base station 110, 111, 114 can transmit a first and secondsignal, the signals for first and second remote stations 123-127respectively, each signal transmitted on the same channel, and eachsignal having a different training sequence. The first remote station123-127 having DARP capability is able to use the training sequences todistinguish the first signal from the second signal and to demodulateand use the first signal, when the amplitudes of the first and secondsignals are substantially within, say, 10 dB of each other.

In summary, FIG. 14 shows that the network assigns the same physicalresources to two mobile stations 125, 127, but allocates differenttraining sequences to them. Each MS will receive its own signal (shownas a solid line in FIG. 14) and that intended for the MS of the otherco-TCH user (shown as a dotted line in FIG. 14). On the downlink, eachmobile station will consider the signal intended for the other mobilestation as a CCI and reject the interference. Thus, two differenttraining sequences may be used to allow the suppression of interferencefrom a signal for another MUROS user.

Joint Detection on the Uplink

The present method and apparatus uses GMSK and the DARP capability ofthe handset to avoid the need for the network to support a newmodulation method. A network may use existing methods on the uplink toseparate each user, e.g., joint detection. It uses co-channel assignmentwhere the same physical resources are assigned to two different remotestations 123-127, but each mobile is assigned a different trainingsequence. On the uplink each remote station 123-127 of the presentmethod and apparatus may use a different training sequence. The networkmay use a joint detection method to separate two users on the uplink.

Speech Codec and Distance to New User

To reduce the interference to other cells, the BS 110, 111, 114 controlsits downlink power relative to the remote or mobile station's distancefrom it. When the MS 123-127 is close to the BS 110, 111, 114, the RFpower level transmitted by the BS 110, 111, 114 to the remote station123-127 on the downlink may be lower than to remote stations 123-127that are further away from the BS 110, 111, 114. The power levels forthe co-channel users are large enough for the caller who is further awaywhen they share the same ARFCN and timeslot. They can both have the samelevel of the power, but this can be improved if the network considersthe distance of co-channel users from the base station 110, 111, 114. Inone example, power may be controlled by identifying the distance andestimate the downlink power needed for the new user 123-127. This can bedone through the timing advance (TA) parameter of each user 123-127.Each user's 123-127 RACH provides this info to the BS 110, 111, 114.

Similar Distances for Users

Another novel feature is to pick a new user with a similar distance as acurrent/existing user. The network may identify the traffic channel(TCH=ARFCN and TS) of an existing user who is in the same cell and atsimilar distance and needs roughly the same power level identifiedabove. Also, another novel feature is that the network may then assignthis TCH to the new user with a different TSC from the existing user ofthe TCH.

Selection of Speech Codec

Another consideration is that the CCI rejection of a DARP capable mobilewill vary depending on which speech codec is used. Thus, the network(NW) may use this criteria and assign different downlink power levelsaccording to the distance to the remote station 123-127 and the codecsused. Thus, it may be better if the network finds co-channel users whoare of similar distance to the BS 110, 111, 114. This is due to theperformance limitation of CCI rejection. If one signal is too strongcompared to the other, the weaker signal may not be detected due to theinterference. Therefore, the network may consider the distance from theBS 110, 111, 114 to new users when assigning co-channels andco-timeslots. The following are procedures which the network may executeto minimize the interference to other cells:

Frequency Hopping to Achieve User Diversity and Take Full Advantage ofDTx

Voice calls can be transmitted with a DTx (discontinuous transmission)mode. This is the mode that the allocated TCH burst can be quiet for theduration of no speech (while one is listening). The benefit of that whenevery TCH in the cell uses DTx is to reduce the overall power level ofthe serving cell on both UL and DL, hence the interference to others canbe reduced. This has significant effect, as normally people do have 40%of time listening. The DTx feature can be used in MUROS mode as well toachieve the know benefit as stated.

There is an extra benefit for MUROS to be achieved when frequencyhopping is used to establish user diversity. When two MUROS users pairtogether, there could be some period of time both MUROS paired users arein DTx. Although this is a benefit to other cells as stated above,neither of the MUROS paired users get the benefit from each other. Forthis reason, when both are in DTx, the allocated resources are wasted.To take the advantage of this potentially helpful DTx period, one canlet frequency hopping to take place so that a group of users are pairingwith each other dynamically on every frame basis. This method introducesuser diversity into the MUROS operation, and reduces the probabilitythat both paired MUROS users are in DTx. It also increases theprobability of having one GMSK on the TCH. Benefits include increasingthe performance of speech calls and maximizing the overall capacity ofthe network (NW).

An example of such case can be illustrated: Suppose the NW identified 8MUROS callers using full rate speech codecs, A, B, C, D, T, U, V, W, whouse similar RF power. Callers A, B, C, D can be non-frequency hopping.In addition, callers A, B, C, D are on the same timeslot, say TS3, butuse four different frequencies, ARFCN f1, f2, f3 and f4. Callers T, U,V, W are frequency hopping. In addition, callers T, U, V, W are on thesame timeslot TS3 and use frequencies f1, f2, f3 and f4 (MobileAllocation (MA) list). Suppose they are given Hopping Sequence Number(HSN)=0, and Mobile Allocation Index Offset (MAIO) 0, 1, 2 and 3respectively. This will let A, B, C, D pair with T, U, V, W in a cyclicform as shown in the table below.

Frame No. 0 1 2 3 4 5 6 7 8 9 10 11 f1 A/T A/W A/V A/U A/T A/W A/V A/UA/T A/W A/V A/U f2 B/U B/T B/W B/V B/U B/T B/W B/V B/U B/T B/W B/V f3C/V C/U C/T C/W C/V C/U C/T C/W C/V C/U C/T C/W f4 D/W D/V D/U D/T D/WD/V D/U D/T D/W D/V D/U D/T

The above is only an example. This form is selected to show how itworks. However it should not be limited to this particular arrangement.It works even better if more randomness of pairing is introduced. Thiscan be achieved by put all of 8 users on frequency hopping on the fourMA list, and give them different HSNs (in the above example 0 to 3) andMAIOs, provided two users are each ARFCN.

Data Transfer

The first method pairs the traffic channel (TCH) being used. In oneexample, this feature is implemented on the network side, with minor orno changes made on the remote station side 123-127. The networkallocates a TCH to a second remote station 123-127 that is already inuse by a first remote station 123-127 with a different TSC. For example,when all the TCHs have been used, any additional service(s) requiredwill be paired with the existing TCH(s) that is (are) using similarpower. For example, if the additional service is a 4D1U data call, thenthe network finds four existing voice call users that use fourconsecutive timeslots with similar power requirement to the additionalnew remote station 123-127. If there is no such match, the network canreconfigure the timeslot and ARFCN to make a match. Then the networkassigns the four timeslots to the new data call which needs 4D TCH. Thenew data call also uses a different TSC. In addition, the uplink powerfor the additional one may brought to be close or to equal the uplinkpower of the remote station 123-127 already using the timeslot.

Assigning a Remote Station 123-127 More than One TSC

If considering data services which use more than one timeslot, all (whenit is even) or all but one (when it is odd) of the timeslots may bepaired. Thus, improved capacity may be achieved by giving the remotestation 123-127 more than one TSC. By using multiple TSCs, the remotestation 123-127 may, in one example, combine its paired timeslots intoone timeslot so that the actual RF resource allocation may be cut byhalf. For example, for 4DL data transfer, suppose that the remotestation 123-127 currently has bursts B1, B2, B3 and B4 in TS1, TS2, TS3and TS4 in each frame. Using the present method, B1 and B2 are assignedone TSC, say TSC0, while B3 and B4 have a different TSC, say TSC1. The,B1 and B2 may be transmitted on TS1, and B3 and B4 may be transmitted onTS2 in the same frame. In this way, the previous 4DL-assignment justuses two timeslots to transmit four bursts over the air. The SAICreceiver can decode B1 and B2 with TSC0, and B3 and B4 with TSC1.Pipeline processing of decoding the four bursts may make this featurework seamlessly with conventional approaches.

Combining Timeslots

Combining one user's even number of timeslots may halve the over the air(OTA) allocation, saving battery energy. This also frees additional timefor scanning and/or monitoring of neighbor cells and system informationupdate for both serving cell and neighbor cells. There are some furtherfeatures on the network side. The network may make the additionalassignment of co-channel, co-time slot (co-TS) based on the distance ofthe new users. Initially the network may use the TCH whose users are ata similar distance. This can be done through timing TA of each user.Each user's RACH provides this info to the BS 110, 111, 114.

Changes in Network Traffic Assignment

The above also means that if two co-channel, co-TS users are moving indifferent directions one moving towards the BS 110, 111, 114 and theother moving away from the BS 110, 111, 114, there will be a point thatone of them will switch to another TCH that has a better match of thepower level. This should not be a problem, as the network may becontinuously re-allocating the users on different ARFCN and TS. Somefurther optimization may be helpful, such as optimizing selection of thenew TSC to be used, as this is related with the frequency reuse patternin the local area. One advantage of this feature is that it uses mainlysoftware changes on network side. e.g., BS 110, 111, 114 and BSC141-144. Changes on network traffic channel assignment may increase thecapacity.

Co-Channel Operation for Both Voice and Data

Further improvements may be made. First, Co-TCH (co-channel andco-timeslot) may be used for voice calls as well as for data calls onthe same TCH to improve capacity-data rate. This feature may be appliedto GMSK modulated data services, such as CS1 to 4 and MCS1 to 4.8 PSK.

Fewer Timeslots Used

This feature may be applied to reuse of co-channel (co-TCH) on datacalls to achieve increased capacity. Two timeslots of data transfer maybe paired and transmitted using one timeslot with two training sequencesused in each of the corresponding bursts. They are assigned to thetarget receiver. This means that 4-timeslot downlink may be reduced to a2-timeslot downlink, which saves power and time for the receiver.Changing from 4-timeslots to 2-timeslots gives the remote station moretime to do other tasks, such as monitoring neighbor cells (NC), whichwill improve the hand off or HO.

The constraints of assignments with respect to Multi-slot Classconfiguration requirements such as Tra, Trb, Tta, Ttb—Dynamic andExtended Dynamic MAC mode rules may be relaxed. This means that thereare more choices for the network to serve the demands from variouscallers in the cell. This reduces or minimizes the number of deniedservice requests. This increases the capacity and throughput from thenetwork point of view. Each user can use less resources withoutcompromise of QoS. More users can be served. In one example, this may beimplemented as a software change on the network side, and the remotestation 123-127 is adapted to accept additional TSCs on top of its DARPcapability. The changes on the network traffic channel assignment mayincrease the capacity-throughput. Use of uplink network resources can beconserved, even while the network is busy. Power can be saved on theremote station 123-127. Better handover performance and less restrictionon network assigning data calls, and improved performance can beachieved.

Dual Carrier

The present method and apparatus may be used with dual carrier inaddition, to improve performance. For improving data rate, there is a3GPP specification which allocates dual carriers from which MS (or UE orremote station 123-127) can get two ARFCNs simultaneously in order toincrease the data rate. Thus, the remote station 123-127 uses more RFresources to get extra data throughput, which intensifies the statedissues above.

Linear GMSK Baseband

One aim of GSM voice services is to achieve the best capacity such thatall users use enough power level, but no greater, to maintain anacceptable error rate so that the user's signal may be detected. Anygreater power would add to unneeded interference experienced by otherusers. Signal quality is affected by i) the distance between the basestation 110, 111, 114 and the remote station 123-127 and ii) the RFenvironment. Therefore, different users 123-127 may be assigneddifferent power levels according to their distance and the RFenvironment. In a GSM based system, power control on the uplink anddownlink is good for limiting unnecessary interference and maintaining agood communication channel.

One advantage of using power control with a multiusers-on-one-time-slot(MUROS) enabled network is that different users 123-127 may betransmitted signals with different power levels to meet their individualneeds. A second advantage is that a non-DARP enabled remote station123-127 may be paired with a DARP enabled remote station 123-127 of thepresent method and apparatus. Then, the non-DARP capable remote station123-127 may be given a signal with a power level a few dB higher thanthe DARP enabled remote station 123-127. A third advantage is that usingpower control allows remote stations 123-127 anywhere in the cell to bepaired.

Transmit Signals at the Same Power Level

DARP enabled mobile stations 123-127 may preferably receive signals atthe same amplitude, regardless of whether one mobile is close and theother one far away. For example, two signals transmitted by one basestation 110, 111, 114, to one mobile 123-127, the path losses for thosesignals, from the BS 110, 111, 114 to the particular mobile, say mobile123, may be the same. Similarly, the path losses for the two signalsfrom BS 110, 111, 114 to mobile 124 may be the same as each other. Thisoccurs because the signals share the same frequency and time slot.

Transmit Signals at Different Power Levels

However, in one example, two MUROS paired remote stations 123-127 mayhave different path losses. Therefore, their signal power levels couldbe different. Hence the BS 110, 111, 114 may send MUROS signals with apower imbalance (say +10 dB to −10 dB).”

Using DARP and Non-DARP Enabled Equipment

Another feature of the present method and apparatus is the use of aMUROS signal by a legacy remote station 123-127 which does not have DARPcapability or MUROS features. The present method and apparatus allows anon-DARP remote station 123-127 to use one of two MUROS signalstransmitted on the same channel. This is achieved by ensuring that theamplitude of the signal intended for the non-DARP remote station 123-127is sufficiently greater than the amplitude of the other MUROS signal.The non-DARP remote station 123-127 does not need to indicate DARPcapability as part of its radio access capability indicating message andthe remote station 123-127 is not required to indicate a MUROSclassmark. It is desirable to pair a MUROS remote station 123-127 with alegacy remote station 123-127 in situations where such an amplitudeimbalance is acceptable or in situations where a second MUROS remotestation 123-127 cannot be identified which is suitable for pairing witha first MUROS remote station 123-127.

It follows that one reason for transmitting the two signals at differentamplitudes is to account for the situation where one of the two remotestations 123-127 are not DARP enabled, and the other is DARP enabled.The non-DARP enabled remote station 123-127 may be supplied a signalhaving more power/amplitude. (In one example, 3 to 8 dB more powerdepending on the training sequences and the corresponding degree ofinterference of the other signal (for the DARP remote station 123-127)at the non-DARP mobile station 123-127.

The range(s) of the remote stations 123-127 is a criteria for choosingremote stations 123-127 for MUROS pairing. The path loss (e.g., the RFenvironment) is another criteria used to determine the amplitudeselected for the signal transmitted to the remote station 123-127 havingthe worst path loss. This also provides the possibility of pairing awider range (in terms of location) of remote stations 123-127 becausethe one near the BS 110, 111, 114 may be given more power than necessarypurely for an acceptable error rate, if there are no pairs which arebetter matched. An ideally matched pair of remote stations 123-127 wouldbe a pair using signals of similar amplitudes.

As stated above, it is preferable for the BS 110, 111, 114 to transmitthe two signals so that each remote station 123-127 receives its wantedsignal above its sensitivity limit. (In one example, it is at least 6 dBabove its sensitivity limit). If the non-DARP remote station 123-127 isclose to sensitivity limit, then the corresponding DARP paired remotestation 123-127 may be selected to be closer to the base station 110,111, 114 i.e., hence have less path loss, otherwise the DARP enabledremote station 123-127 may lose its signal since its signal is receivedat a lower amplitude than the amplitude of the other signal. Differentcodecs may also be used to adapt the remote stations 123-127 to enhanceperformance when a non-DARP enabled remote station 123-127 is usingMUROS enabled equipment of the present method and apparatus.

Transmitting Two Signals

Two signals may be transmitted by a base station 110, 111, 114 using oneof two approaches. (Other approaches may also be possible). In the twoalternative representations or examples, two GMSK signals may becombined with different amplitudes, A₁ for the first signal and A₂, forthe second. The ratio of amplitudes (or amplitude ratio) corresponds tothe ratio of amplitudes for the two transmitted (and received) signals.The path loss between the BS 110, 111, 114 and a given remote station123-127 is likely to be the same or near-identical for the two signalstransmitted by the BS 110, 111, 114. As discussed above, the BS 110,111, 114 transmits the signals at suitable amplitudes so that eachremote station 123-127 of the present method and apparatus receives itsown signal at a high enough amplitude and two signals have an amplituderatio such that the two signals corresponding to the two TSCs may bedetected. The signals may be both transmitted by one transmitter of abase station 110, 111, 114 on the same channel (comprising only onetimeslot and only one frequency) with both signals received by thereceiver of a first remote station 123-127 in the amplitude ratio andboth signals received by the receiver of a second remote station 123-127in the same amplitude ratio. The ratio of amplitudes can be expressed asthe product of A₂ divided by A₁ or the product of A₁ divided by A₂ Theratio is expressed in decibels as 20*log 10(A₂/A₁) or 20*log 10(A₁/A₂).The ratio can be adjusted and preferentially has a magnitude of eithersubstantially 0 dB or substantially between 8 dB and 10 dB. The ratiocan be less than one or greater than one and hence, the ratio expressedin dB can be correspondingly positive or negative.

In a first approach or example, steps can be carried out in accordancewith the flow diagram shown in FIG. 21A. The two signals may be GMSKmodulated (step 2110) and added together (step 2140), each with arespective power level chosen to offset attenuation due to the differentsignal distances and environments. That is, each signal is multiplied bya its own gain (step 2130). The gains may be chosen to be in the ratioR=A2/A1, which yields the correct amplitude (hence power) ratio for thetwo signals. This is what yields the 8-10 dB ratio discussed above. Ifboth remote stations are DARP enabled, it is preferred in one examplefor the ratio to be unity (0 dB). For one remote station 123-127 to beDARP enabled and the other non-DARP enabled, it is preferred in oneexample for the ratio to be 8-10 dB in favour of the non-DARP enabledremote station 123-127. This may be referred to as differential powercontrol and it may be implemented either at baseband or at RF, or both.Further (common) power control can be applied to both signals equally(to account for range, path loss of the remote station 123-127 requiringhighest amplitude (e.g. the remote station 123-127 may be further away).This additional power control may be applied partly at baseband andpartly at RF, or only at RF. At baseband, common power control isapplied to both signals by the equal scaling of gains A1 and A2, e.g.multiplying them both by 1.5. Common power control at RF is normallyexecuted in the power amplifier (PA) 1830. It could also be partlyexecuted in the RF modulator 1825.

Also, one of the signals may be phase shifted by π/2 relative to theother signal The π/2 phase shift is shown as step 2120 of FIG. 21A, inblock 1810 of FIGS. 15, 16, and 19, and in blocks 1818 and 1819 of FIGS.17 and 18. The added signals are then transmitted (step 2150). Anexample apparatus is shown in FIG. 15. Preferably, one of the twosignals is shifted in phase relative to the other signal prior totransmission, and preferably by 90 degrees, i.e., π/2 radians. Howeverthe present method and apparatus may work with any phase shift betweenthe signals including zero phase shift. If more than two signals aretransmitted, each signal can be offset in phase from the others. Forexample, for three signals each can be offset from the others by 120degrees. In FIG. 21A, the steps of phase shifting and amplifying by again may be done in either order as illustrated where steps 2120 and2130 are reversed in the flowchart of FIG. 21C compared to FIG. 21A.FIG. 15 discloses an apparatus to combine two signals. It comprises twoGMSK baseband modulators 1805 having at least one input and at least oneoutput, whereby the signals are modulated. One amplifier 1815 isconnected in series with each GMSK modulator 1805, whereby the twosignals are multiplied by a respective amplitude, A₁ for the firstsignal and A₂, for the second. signal where A1 is equal to cos α and A2is equal to sin α. The output of each amplifier 1815 is combined in acombiner (adder) 1820, and a phase shifter 1810 is preferably operablyconnected between one of the series combinations of baseband modulator1805 and amplifier 1815, so that one of said signals is phase shiftedwith respect to the other signal. The output of the combiner 1820 isinput into a RF modulator/power amplifier module 1823, whereby thecombined signals are RF modulated and transmitted. By RF modulated, itis meant that the signals are upconverted from baseband to RF frequency.It is noted that the phase shifter 1810 may be operably connectedbetween one amplifier 1815 and the combiner 1820.

FIGS. 16-18 disclose second, third and fourth examples of the apparatusfor combining and transmitting two signals with different amplitudes. InFIG. 16, the RF modulator & power amplifier 1823 is represented by aseries connection of a RF modulator 1825 and power amplifier 1830. Theexample shown in FIG. 17 shows the use of GMSK baseband modulators 1805and one RF modulator 1862. The first and second data are basebandmodulated by baseband modulators 1805. Baseband modulators 1805 eachcomprise a differential encoder, an integrator and a Gaussian lowpassfilter 1811. The outputs of the respective baseband modulators 1805 areeach a digital value representing the phase of the GMSK modulated signal(φ(t) for the first signal and φ′(t) for the second signal). Block 1816comprises a function which produces the cosine of said phase of thefirst signal and multiples the cosine by a gain A1 to provide an outputsignal, A1 cos φ(t) at the output of the block 1816.

Block 1818 comprises a function which adds a phase shift of pi/2 radians(90 degrees) to the phase of the second signal, produces the cosine ofthe resulting phase and multiples the cosine by a gain A2 to provide anoutput signal, A2 cos (φ′(t)+90) at the output of the block 1818.

Block 1817 comprises a function which produces the sine of said phase ofthe first signal and multiples the sine by a gain A1 to provide anoutput signal, A1 sin φ(t) at the output of the block 1817.

Block 1819 comprises a function which adds a phase shift of pi/2 radians(90 degrees) to the phase of the second signal, produces the sine of theresulting phase and multiples the sine by a gain A2 to provide an outputsignal, A2 sin (φ′(t)+90) at the output of the block 1819.

The outputs of blocks 1816 and 1818 are summed/combined by combiner 1807to produce a summed I (in-phase) GMSK modulated baseband signal. Theoutputs of blocks 1817 and 1819 are summed/combined by combiner 1827 toproduce a summed Q (quadrature-phase) GMSK modulated baseband signal.

Preferably, as shown, all operations and signals in blocks 1816-1819,1807 and 1827, are digital, and so the outputs of the combiners 1807,1827 are also digital values. Alternatively, some of the functions couldbe performed by analogue circuitry by the use of digital-to-analogueconversion, etc.

The summed GMSK modulated baseband digital signals output from combiners1807, 1827 are each input to a digital-to-analogue converter (DAC orD/A) 1850, 1852 and suitably lowpass filtered (filter not shown) to formI and Q inputs to the RF modulator 1862, which upconverts the basebandsignals onto a carrier frequency, the carrier frequency provided bylocal oscillator 421, to form a transmitted signal.

The example shown in FIG. 18 shows the use of two GMSK basebandmodulators 1805 and two RF modulators 1862, 1864. The output of each RFmodulator 1862, 1864, one RF modulator 1862, 1864 for each of the firstand second data respectively, are summed/combined with each other, incombiner 1828, for transmission. Both FIGS. 17 and 18 disclose two GMSKbaseband modulators 1805, each comprising a differential encoder 1807,an integrator 1809 operably connected to said differential encoder 1807,and a Gaussian low pass filter 1811 operably connected to saidintegrator 1809

In FIGS. 18 and 19 a −π/2 phase shift is introduced to the lo signal bythe outputs of the splitter 1812. Thus, the LO is split into in-phaseand quadrature-phase and input to each of two mixers/multipliers1840-1844, 1848.

FIG. 19 illustrates an alternative approach or example for combining(step 2180) two signals by mapping both users' data onto the I and Qaxis respectively of a QPSK constellation. According to this approach,the data of users 1 and 2 is mapped to the I and Q axis respectively ofa QPSK constellation (step 2170), with π/2 progressive phase rotation(step 2177) on every symbol (like EGPRS 3π/8 rotation on every symbol,but with pi/2 instead of 3π/8) with each user's signal power leveldetermined by the A₁ and A₂ gains (step 2175). Amplifier gain for the Isignal (for user 1) is A₁ which is equal to the cosine of alpha, α.Amplifier gain for the Q signal is A₂ which is equal to the sine ofalpha. Alpha is the angle whose tangent is the amplitude ratio. Thebaseband modulators 1805 comprise a binary phase shift keying (BPSK)baseband modulator 1805 for a first signal represented on an I axis anda BPSK baseband modulator 1805 for a second signal represented on a Qaxis. The transmit I and Q signals which are input to phase rotator 1820of FIG. 19, may be filtered (step 2185) before or after phase shifting(step 2177), by means of a linear Gaussian filter or pulse-shapingfilter 1821 (e.g., for use with EGPRS 8 PSK modulation) to satisfy theGSM spectrum mask criteria. FIG. 19 shows a suitable pulse-shapingfilter 1821 operably connected between said phase rotator 1820 and a RFmodulator/power amplifier 1823. The RF modulator and PA block 1823 actsto RF modulate and amplify the combined I and Q signals for transmissionvia the antenna.

The QPSK constellation diagram is shown in FIG. 20.

The steps executed in the two approaches (GMSK or QPSK based) aredisclosed in the flowcharts of FIGS. 21A and 21B respectively. In FIG.21A, the steps of phase shifting and amplifying by a gain may be done ineither order as illustrated in FIG. 21C where the order of steps 2120and 2130 are reversed compared to the flowchart of FIG. 21A.

With both of the approaches, when a MUROS enabled BS 110, 111, 114 sendsa RF burst on the downlink channel, the BS 110, 111, 114 controls twoparameters:

First, the I and Q data streams are normalized, which enhances theresolution and dynamic range of the digital-to-analog controller (DAC)1850, 1852 used.

Second, the power level used for the signal burst containing both the Iand Q signals is controlled. This is used to determine the gain for thepower amplifier (PA) (see below).

The following are additional steps which may be taken by a MUROS-enabledbase station, as compared to a legacy base station, to use the presentmethod and apparatus. See FIG. 22 for a simplified flow diagram.

First, use the path loss of the two signals to derive the power level tobe used for both co-TCH callers, say power level 1, P1, for user 1 andpower level 2, P2, for user 2 respectively (In this example, the powerlevel is expressed in Watts, not dBm) (step 2210)

Second, calculate the amplitude ratio R of the two power levels (step2220):R=√{square root over (P2/P1)}

Third, determine the gains, G1 and G2, for the two users or callers,user 1 and user 2 respectively (step 2230): In one example, for user 1,G1=A₁=cos(α), and for user 2, G2=A₂=sin(α), while α=arc tangent (R).Also, A₂/A₁=sin(α)/cos(α)=tan(α)=R.

Fourth, determine the gain for the power amplifier by considering thepower level:P=P1+P2.  (step 2240)

The present method and apparatus combines two signals that may havedifferent phases and power levels, so that: 1) Each user may receive awanted signal having the required amplitude together with an unwantedsignal, such that the amplitude of the unwanted signal is less than theamplitude at which the unwanted signal would cause unacceptableinterference to the wanted signal. This may avoid excessive amplitudethat could interfere with others in another cell. However, in somecases, a lower power remote station 123-127 (lower power is used becauseit is nearer to the base station 110, 111, 114) can have higher powerinstead (more than the remote station 123-127 needs) in order to pairwith a remote station 123-127 that is further away from the base station110, 111, 114). The zero-crossing of the modulation ‘eye diagram’ may beavoided, which may help avoid AM-PM conversion distortion and lowsignal-to-noise ratio (SNR). In addition, a legacy (non-MUROS) remotestation, either non-DARP enabled or DARP enabled, may be used with theMUROS enabled network, i.e., base station 110, 111, 114 or base stationcontroller 140-143.

This method may be stored as executable instructions in software storedin memory 962 which are executed by processor 960 in the BTS as shown inFIG. 23. It may also be stored as executable instructions in softwarestored in memory which are executed by a processor in the BSC 140-143.The remote station 123-127 uses the TSC it is instructed to use.

Signaling

Because the signalling channel has good coding and FEC capability, itonly needs a minimal signal quality to detect the desired signal. Anyhigher signal power levels than that would waste power and createinterference to other remote stations 123-127. In this way eachcommunication will drop the power level to minimize interference toanother remote station 123-127 in the network, while maintaining anacceptable BER which may processed by FEC to allow detection of thedesired signal.

Benefits of the present method and apparatus (See step 1710 of flowchartin FIG. 36). (See step 1720 of flowchart in FIG. 36). include:

Minimizing unnecessary interferences through out the network.

Avoiding excess interference in the network between signals fordifferent users; Allowing the network to for support potential increasedcapacity.

Allowing the network to support more calls and achieve improvedcapacity.

Saving battery life and prolong the talk time and standby time.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted as one or more instructions or code on a computer-readablemedium. Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The methods described herein may be implemented by various means. Forexample, these methods may be implemented in hardware, firmware,software, or a combination thereof. For a hardware implementation, theprocessing units used to detect for ACI, filter the I and Q samples,cancel the CCI, etc., may be implemented within one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, electronic devices, other electronicunits designed to perform the functions described herein, a computer, ora combination thereof.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples described herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

Those of ordinary skill in the art would understand that information andsignals may be represented using any of a variety of differenttechnologies and techniques. For example, data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof.

Those of ordinary skill would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a Digital SignalProcessor (DSP), an Application Specific Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in Random Access Memory (RAM), flashmemory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM),Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal. In thealternative, the processor and the storage medium may reside as discretecomponents in a user terminal.

Therefore, the present invention is not to be limited except inaccordance with the following claims.

The invention claimed is:
 1. A method of combining two signals,comprising: modulating the two signals; multiplying the two signals by again; phase shifting the two signals; adding the two signals together toform an added signal; and transmitting the added signal, wherein a firstsignal of the two signals is transmitted at a higher amplitude than anamplitude of a second signal of the two signals, wherein the firstsignal includes data for a non-downlink advanced receiver performance(DARP) enabled remote station, wherein the second signal includes datafor a DARP enabled remote station, and wherein the higher amplitude ofthe first signal allows the non-DARP enabled remote station to treat thesecond signal as interference.
 2. The method according to claim 1,wherein said gain is a ratio of amplitudes comprising a product of A₂divided by A₁, where A₁ is an amplitude for the first signal and A₂ isan amplitude for the second signal.
 3. The method according to claim 1,wherein said phase shifting comprises phase shifting one of the twosignals by π/2 on every inphase and quadrature of the two signals. 4.The method according to claim 1, further comprising: mapping the twosignals to an inphase and quadrature axis; and filtering the twosignals.
 5. The method according to claim 2, wherein said ratioexpressed in decibels is 20*log 10(A₂/A₁), where said ratio expressed indecibels is between 8-10 dB.
 6. The method according to claim 4, whereintwo signals are mapped to the inphase and quadrature axis of a QPSKconstellation, with π/2 progressive phase rotation on every symbol. 7.The method according to claim 4, wherein said gain is a ratio ofamplitudes comprising a product of A₂ divided by A₁, where A₁ is anamplitude for an inphase signal which is equal to a cosine of alpha,wherein alpha is an angle whose tangent is the amplitude ratio of thefirst signal and the second signal, and A₂ is an amplitude for aquadrature signal which is equal to a sine of alpha.
 8. The methodaccording to claim 4, further comprising sharing signals on a singlechannel; comprising: setting up a new connection; selecting an used timeslot on a channel frequency for said new connection to share with anexisting connection; selecting a different training sequence for saidnew connection from said existing connection's training sequence; andusing both said training sequences in a same time slot on a same channelfrequency by one base station.
 9. The method according to claim 4,further comprising producing first and second signals which share achannel, comprising: generating a first data and a second data;generating a first training sequence and a second training sequence;combining the first training sequence with the first data to produce afirst combined data and combining the second training sequence with thesecond data to produce a second combined data; modulating andtransmitting both said first combined data and said second combined datausing a same channel frequency and a same time slot to produce first andsecond transmitted signals, and using both said training sequences in asame time slot on a same channel frequency by one base station.
 10. Themethod according to claim 7, wherein said step of filtering the addedsignals comprises filtering the added signals with a linear Gaussianfilter used for EGPRS 8 PSK modulation to satisfy a GSM spectrum maskcriteria.
 11. An apparatus to combine two signals, comprising: at leastone baseband modulator having at least one input and at least oneoutput, whereby the two signals are modulated; at least one amplifierhaving an input and at least one output, wherein said at least one inputis operably connected to said output of said at least one basebandmodulator, whereby the two signals are multiplied by a gain; and atleast one combiner having at least one input and at least one output,wherein said at least one input is operably connected to said at leastone output of said at least one amplifier, whereby the two signals arecombined, wherein a first signal of the two signals is transmitted at ahigher amplitude than a second signal of the two signals, wherein thefirst signal includes data for a non-downlink advanced receiverperformance (DARP) enabled remote station, wherein the second signalincludes data for a DARP enabled remote station, and wherein the higheramplitude of the first signal allows the non-DARP enabled remote stationto treat the second signal as interference.
 12. The apparatus to combinetwo signals according to claim 11, further comprising a RFmodulator/power amplifier having at least one input and at least oneoutput, wherein said at least one input is operably connected to said atleast one output of said combiner, whereby the two signals aretransmitted.
 13. The apparatus to combine two signals according to claim11, further comprising a series connection of an RF modulator and poweramplifier operably connected to said at least one output of saidcombiner, whereby the two signals are transmitted.
 14. The apparatus tocombine two signals according to claim 11, further comprising a phaseshifter operably connected between said at least one amplifier and saidat least one baseband modulator.
 15. The apparatus to combine the twosignals according to claim 11, further comprising a phase shifter,wherein said at least one combiner is operably connected between said atleast one amplifier and said phase shifter.
 16. The apparatus to combinetwo signals according to claim 11, wherein said at least one basebandmodulator having at least one input and at least one output is a GMSKbaseband modulator.
 17. The apparatus to combine two signals accordingto claim 11, wherein said at least one baseband modulator having atleast one input and at least one output comprises a BPSK basebandmodulator on an inphase axis and a BPSK baseband modulator on aquadrature axis.
 18. The apparatus according to claim 11, wherein aphase shifter phase shifts one of the two signals with a π/2 progressivephase rotation on every symbol with respect to another of the twosignals.
 19. The apparatus to combine two signals according to claim 11,wherein said at least one baseband modulator comprises: a differentialencoder; an integrator operably connected to said differential encoder;and a Gaussian low pass filter operably connected to said integrator.20. The apparatus to combine two signals according to claim 11, whereinsaid at least one amplifier comprises: a first amplifier with a gain ofA₁ multiplied by a cosine of alpha, wherein alpha is an angle whosetangent is the amplitude ratio of the first signal and the secondsignal; a second amplifier with a gain of A₁ multiplied by a sine ofalpha; a third amplifier with a gain of A₂ multiplied by a cosine ofalpha +π/2; and a fourth amplifier with a gain of A₂ multiplied by asine of alpha +π/2.
 21. The apparatus to combine two signals accordingto claim 11, further comprising: a filter operably connected betweensaid combiner and a RF modulator/power amplifier; and a phase shifteroperably connected to said at least one baseband modulator.
 22. Theapparatus to combine two signals according to claim 19, wherein said atleast one amplifier comprises: a first amplifier with a gain of A₁multiplied by a cosine of alpha, wherein alpha is an angle whose tangentis the amplitude ratio of the first signal and the second signal; asecond amplifier with a gain of A₁ multiplied by a sine of alpha; athird amplifier with a gain of A₂ multiplied by a cosine of alpha; +π/2and a fourth amplifier 1819 with a gain of A₂ multiplied by a sine ofalpha +π/2.
 23. The apparatus to combine two signals according to claim22, wherein said at least one baseband modulator having at least oneinput and at least one output comprises a BPSK baseband modulator on aninphase axis and a BPSK baseband modulator on a quadrature axis.
 24. Theapparatus to combine two signals according to claim 22, wherein saidfilter is a linear Gaussian filter.
 25. The apparatus to combine twosignals according to claim 23, wherein said filter is a linear Gaussianfilter.
 26. The apparatus to combine two signals according to claim 25,further comprising at least one RF modulator comprising an oscillator, asplitter having an input and a first and a second output separated by aphase shift operably connected to said oscillator; and a plurality ofmultipliers each having at least one input and at least one output,wherein said at least one input of said first multiplier is operablyconnected to an output of a first amplifier, said at least one input ofa second multiplier is operably connected to an output of said secondamplifier, said at least one input of a third multiplier is operablyconnected to an output of said third amplifier, and said at least oneinput of a fourth multiplier is operably connected to an output of saidfourth amplifier.
 27. The apparatus to combine two signals according toclaim 25, further comprising: at least one RF modulator comprising anoscillator, a splitter having an input and a first and a second outputseparated by a phase shift operably connected to said oscillator; aplurality of multipliers each having at least one input and at least oneoutput, comprising: a first multiplier having said at least one inputoperably connected to said first amplifier and a −π/2 phase shiftedoutput of said splitter and having said at least one output operablyconnected to one input of a first combiner; a second multiplier havingsaid at least one input operably connected to said second amplifier anda zero degree phase shifted output of said splitter and having said atleast one output operably connected to another input of said firstcombiner; a third multiplier having said at least one input operablyconnected to said third amplifier and said −π/2 phase shifted output ofsaid splitter and having said at least one output operably connected toone input of a second combiner; and a fourth multiplier having said atleast one input operably connected to said fourth amplifier and saidzero degree phase shifted output of said splitter and having said atleast one output operably connected to said another input of said secondcombiner; and a third combiner having at least one input and at leastone output, wherein said at least one input is operably connected tosaid outputs of said first combiner and said second combiner.
 28. Theapparatus to combine two signals according to claim 25, wherein said atleast one combiner comprises a first combiner having at least one inputand at least one output, wherein said at least one input is operablyconnected to said first amplifier and said third amplifier; and a secondcombiner having at least one input and at least one output, wherein saidat least one input is operably connected to said second amplifier andsaid fourth amplifier; and wherein said apparatus to combine two signalsfurther comprises a RF modulator having a plurality of inputs and aplurality of outputs; a first digital-to-analog converter operablyconnected between said at least one output of said first combiner andone input of said RF modulator; a second said digital-to-analogconverter operably connected between said at least one output of saidsecond combiner and another input of said RF modulator; and a thirdcombiner having at least one input and at least one output, wherein saidat least one input is operably connected to said outputs of said RFmodulator.
 29. The apparatus to combine two signals according to claim28, wherein: said RF modulator comprises an oscillator, a splitterhaving an input operably connected to said oscillator and a −π/2 phaseshifted output and a zero degree output, and a plurality of multipliers,wherein said −π/2 phase shifted output of said splitter is operablyconnected to one input of said first multiplier; and said zero degreephase shifted output of said splitter is operably connected to anotherinput of said second multiplier.
 30. A base station, comprising: acontroller processor; an antenna; a duplexer switch operably connectedto said antenna; a receiver front end operably connected to saidduplexer switch; a receiver demodulator operably connected to saidreceiver front end; a channel decoder and de-interleaver operablyconnected to said receiver demodulator and said controller processor; abase station controller interface operably connected to said controllerprocessor; a coder and interleaver operably connected to said controllerprocessor; a transmitter modulator operably connected to said coder andinterleaver; a transmitter front end module operably connected to saidtransmitter modulator and operably connected to said duplexer switch; adata bus operably connected between said controller processor and saidchannel decoder and de-interleaver, said receiver demodulator, saidreceiver front end, said transmitter modulator and said transmitterfront end; and an apparatus to combine two signals, comprising: at leastone baseband modulator having at least one input and at least oneoutput, whereby the two signals are modulated; at least one amplifierhaving an input and at least one output, wherein said at least one inputis operably connected to said output of said at least one output of saidat least one baseband modulator, whereby the two signals are multipliedby a gain; and at least one combiner having at least one input and atleast one output, wherein said at least one input is operably connectedto said at least one output of said at least one amplifier, whereby thetwo signals are combined, wherein a first signal of the two signals istransmitted at a higher amplitude than a second signal of the twosignals, wherein the first signal includes data for a non-downlinkadvanced receiver performance (DARP) enabled remote station, wherein thesecond signal includes data for a DARP enabled remote station, andwherein the higher amplitude of the first signal allows the non-DARPenabled remote station to treat the second signal as interference. 31.The base station according to claim 30, further comprising a RFmodulator/power amplifier having at least one input and at least oneoutput, wherein said at least one input is operably connected to said atleast one output of said combiner, whereby the two signals aretransmitted.
 32. The base station according to claim 30, furthercomprising a series connection of an RF modulator and power amplifieroperably connected to said at least one output of said combiner, wherebythe two signals are transmitted.
 33. The base station according to claim30, further comprising a phase shifter operably connected between saidat least one amplifier and said at least one baseband modulator.
 34. Thebase station according to claim 30, further comprising a phase shifter,wherein said at least one combiner is operably connected between said atleast one amplifier and said phase shifter.
 35. The base stationaccording to claim 30, wherein said at least one baseband modulatorhaving at least one input and at least one output is a GMSK basebandmodulator.
 36. The base station according to claim 30, wherein said atleast one baseband modulator having at least one input and at least oneoutput comprises a BPSK baseband modulator on an inphase axis and a BPSKbaseband modulator on a quadrature axis.
 37. The base station accordingto claim 30, wherein a phase shifter phase shifts one of the two signalswith a π/2 progressive phase rotation on every symbol with respect toanother of the two signals.
 38. The base station according to claim 30,wherein said at least one baseband modulator comprises: a differentialencoder; an integrator operably connected to said differential encoder;and a Gaussian low pass filter operably connected to said integrator.39. The base station according to claim 30, wherein said at least oneamplifier comprises: a first amplifier with a gain of A₁ multiplied by acosine of alpha, wherein alpha is an angle whose tangent is theamplitude ratio of the first signal and the second signal; a secondamplifier with a gain of A₁ multiplied by a sine of alpha; a thirdamplifier with a gain of A₂ multiplied by a cosine of alpha +π/2; and afourth amplifier with a gain of A₂ multiplied by a sine of alpha +π/2.40. The base station according to claim 30, further comprising: a filteroperably connected between said combiner and a RF modulator/poweramplifier; and a phase shifter operably connected to said at least onebaseband modulator.
 41. The base station according to claim 30, furthercomprising: a plurality of data sources; at least one sequence generatorhaving a plurality of outputs; a plurality of combiners, each having aplurality of inputs and at least one output, wherein a first of saidinputs is operably connected to one of said outputs of one of said datasources and a second of said inputs is operably connected to one of saidoutputs of said sequence generator, whereby at least one trainingsequence is combined with at least one data to produce at least onecombined data; and said transmitter modulator having a plurality ofinputs and at least one output.
 42. The base station according to claim30, further comprising software stored in memory, wherein said memorycomprises instructions to produce first and second signals which share achannel, comprising: generate a first data and a second data; generate afirst training sequence and a second training sequence; combine thefirst training sequence with the first data to produce a first combineddata; combine the second training sequence with the second data toproduce a second combined data; modulate and transmit both said firstcombined data and said second combined data using a same carrierfrequency and a same time slot to produce first and second transmittedsignals, and use both said training sequences, in a same time slot onthe same carrier frequency by the base station.
 43. The base station toclaim 30, further comprising software stored in memory, wherein saidsoftware comprises instructions to share signals on a single channel;comprising: set up a new connection; select an used time slot for saidnew connection to share with an existing connection; select a differenttraining sequence code for said new connection from said existingconnection's training sequence; and use both said training sequences ina same time slot on the same carrier frequency by the base station. 44.The base station according to claim 38, wherein said at least oneamplifier comprises: a first amplifier with a gain of A₁ multiplied by acosine of alpha, wherein alpha is an angle whose tangent is theamplitude ratio of the first signal and the second signal; a secondamplifier with a gain of A₁ multiplied by a sine of alpha; a thirdamplifier with a gain of A₂ multiplied by a cosine of alpha +π/2; and afourth amplifier with a gain of A₂ multiplied by a sine of alpha +π/2.45. The base station according to claim 40, wherein said at least onebaseband modulator having at least one input and at least one outputcomprises a BPSK baseband modulator on an inphase axis and a BPSKbaseband modulator on a quadrature axis.
 46. The base station accordingto claim 40, wherein said filter is a linear Gaussian filter.
 47. Thebase station according to claim 45, wherein said filter is a linearGaussian filter.
 48. The base station according to claim 46, furthercomprising at least one RF modulator comprising an oscillator, asplitter having an input and a first and a second output separated by aphase shift operably connected to said oscillator; and a plurality ofmultipliers each having at least one input and at least one output,wherein said at least one input of a first multiplier is operablyconnected to an output of said first amplifier, said at least one inputof a second multiplier is operably connected to an output of said secondamplifier, said at least one input of a third multiplier is operablyconnected to an output of said third amplifier, and said at least oneinput of a fourth multiplier is operably connected to an output of saidfourth amplifier.
 49. The base station according to claim 47, furthercomprising at least one RF modulator comprising: an oscillator, asplitter having an input and a first and a second output separated by aphase shift operably connected to said oscillator; and a plurality ofmultipliers each having at least one input and at least one output,comprising: a first multiplier having said at least one input operablyconnected to said first amplifier and a −π/2 phase shifted output ofsaid splitter and having said at least one output operably connected toone input of a first combiner; a second multiplier having said at leastone input operably connected to said second amplifier and a zero degreephase shifted output of said splitter and having said at least oneoutput operably connected to another input of said first combiner; athird multiplier having said at least one input operably connected tosaid third amplifier and said −π/2 phase shifted output of said splitterand having said at least one output operably connected to one input of asecond combiner; and a fourth multiplier having said at least one inputoperably connected to said fourth amplifier and said zero degree phaseshifted output of said splitter and having said at least one outputoperably connected to said another input of said second combiner; and athird combiner having at least one input and at least one output,wherein said at least one input is operably connected to said outputs ofsaid first combiner and said second combiner.
 50. The base stationaccording to claim 47, wherein said at least one combiner comprises afirst combiner having at least one input and at least one output,wherein said at least one input is operably connected to a firstamplifier and a third amplifier; and a second combiner having at leastone input and at least one output, wherein said at least one input isoperably connected to a second amplifier and a fourth amplifier; andwherein said apparatus to combine two signals further comprises a RFmodulator having a plurality of inputs and a plurality of outputs; afirst digital-to-analog converter operably connected between said atleast one output of said first combiner and one input of said RFmodulator; a second said digital-to-analog converter operably connectedbetween said at least one output of said second combiner and anotherinput of said RF modulator; and a third combiner having at least oneinput and at least one output, wherein said at least one input isoperably connected to said outputs of said RF modulator.
 51. The basestation according to claim 50, wherein said RF modulator comprises anoscillator, a splitter having an input operably connected to saidoscillator and a −π/2 phase shifted output and a zero degree phaseshifted output, and a plurality of multipliers, wherein said −π/2 phaseshifted output of said splitter is operably connected to one input ofsaid first multiplier, and said zero degree phase shifted output of saidsplitter is operably connected to another input of said secondmultiplier.
 52. An apparatus for combining two signals, comprising:means for modulating the two signals; means for multiplying the twosignals by a gain; means for phase shifting the two signals; means foradding the two signals together; and means for transmitting the addedsignals, wherein a first signal of the two signals is transmitted at ahigher amplitude than a second signal of the two signals, wherein thefirst signal includes data for a non-downlink advanced receiverperformance (DARP) enabled remote station, wherein the second signalincludes data for a DARP enabled remote station, and wherein the higheramplitude of the first signal allows the non-DARP enabled remote stationto treat the second signal as interference.
 53. The apparatus accordingto claim 52, wherein said gain is a ratio of amplitudes comprising aproduct of A₂ divided by A₁, where A₁ is an amplitude for the firstsignal and A₂ is an amplitude for the second signal.
 54. The apparatusaccording to claim 52, wherein said means for phase shifting comprisesmeans for phase shifting one of the two signals by π/2 on every inphaseand quadrature of the two signals.
 55. The apparatus according to claim52, further comprising: means for mapping the two signals to inphase andquadrature axis; and means for filtering the two signals.
 56. Theapparatus according to claim 53, wherein said ratio expressed indecibels is 20*log 10(A₂/A₁), where said ratio expressed in decibels isbetween 8-10 dB.
 57. The apparatus according to claim 55, wherein thetwo signals are mapped to the inphase and quadrature axis of a QPSKconstellation, with π/2 progressive phase rotation on every symbol. 58.The apparatus according to claim 55, wherein said gain is a ratio ofamplitudes comprising a product of A₂ divided by A₁, where A₁ is anamplitude for an inphase signal which is equal to a cosine of alpha,wherein alpha is an angle whose tangent is the amplitude of the ratio,and A₂ is an amplitude for a quadrature signal which is equal to a sineof alpha.
 59. The apparatus according to claim 55, further comprisingmeans for sharing signals on a single channel; comprising: means forsetting up a new connection; means for selecting an used time slot on achannel frequency for said new connection to share with an existingconnection; means for selecting a different training sequence for saidnew connection from said existing connection's training sequence; andmeans for using both said training sequences in a same time slot on asame channel frequency by one base station.
 60. The apparatus accordingto claim 55, further comprising means for producing first and secondsignals which share a channel, comprising: means for generating a firstdata and a second data; means for generating a first training sequenceand a second training sequence; means for combining the first trainingsequence with the first data to produce a first combined data andcombining the second training sequence with the second data to produce asecond combined data; means for modulating and transmitting both saidfirst combined data and said second combined data using a same channelfrequency and a same time slot to produce first and second transmittedsignals, and means for using both said training sequences in a same timeslot on a same channel frequency by one base station.
 61. The apparatusaccording to claim 56, further comprising means for filtering the addedsignals with a linear Gaussian filter used for EGPRS 8 PSK modulation tosatisfy a GSM spectrum mask criteria.
 62. A computer program product,comprising: a non-transitory computer-readable medium comprising: codefor causing a computer to combine two signals, comprising instructionsto: modulate the two signals; multiply the two signals by a gain; phaseshift the two signals; add the two signals together; and transmit theadded signals, wherein a first signal of the two signals is transmittedat a higher amplitude than a second signal of the two signals, whereinthe first signal includes data for a non-downlink advanced receiverperformance (DARP) enabled remote station, wherein the second signalincludes data for a DARP enabled remote station, and wherein the higheramplitude of the first signal allows the non-DARP enabled remote stationto treat the second signal as interference.
 63. The computer programproduct according to claim 62, wherein said gain is a ratio ofamplitudes comprising a product of A₂ divided by A₁, where A₁ is anamplitude for the first signal and A₂ is an amplitude for the secondsignal.
 64. The computer program product according to claim 62, whereinsaid instruction to phase shift comprises means for phase shifting oneof the two signals by π/2 on every inphase and quadrature of the twosignals.
 65. The computer program product according to claim 62, furthercomprising: instructions to map the two signals to an inphase andquadrature axis; and instructions to filter the two signals.
 66. Thecomputer program product according to claim 63, wherein said ratioexpressed in decibels is 20*log 10(A₂/A₁), where said ratio expressed indecibels is between 8-10 dB.
 67. The computer program product accordingto claim 65, wherein the two signals are mapped to the inphase andquadrature axis of a QPSK constellation, with π/2 progressive phaserotation on every symbol.
 68. The computer program product according toclaim 65, wherein said gain is a ratio of amplitudes comprising aproduct of A₂ divided by A₁, where A₁ is an amplitude for an inphasesignal which is equal to a cosine of alpha, wherein alpha is an anglewhose tangent is the amplitude ratio of the first signal and the secondsignal, and A₂ is an amplitude for a quadrature signal which is equal toa sine of alpha.
 69. The computer program product according to claim 65,further comprising instructions to share signals on a single channel;comprising: set up a new connection; select an used time slot on achannel frequency for said new connection to share with an existingconnection; select a different training sequence for said new connectionfrom said existing connection's training sequence; and use both saidtraining sequences in a same time slot on a same channel frequency byone base station.
 70. The computer program product according to claim65, further comprising instructions to produce first and second signalswhich share a channel, comprising: generate a first data and a seconddata; generate a first training sequence and a second training sequence;combine the first training sequence with the first data to produce afirst combined data and combining the second training sequence with thesecond data to produce a second combined data; modulate and transmittingboth said first combined data and said second combined data using a samechannel frequency and a same time slot to produce first and secondtransmitted signals, and use both said training sequences in a same timeslot on a same channel frequency by one base station.
 71. The computerprogram product according to claim 66, wherein said instruction tofilter the added signals comprises filter the added signals with alinear Gaussian filter used for EGPRS 8 PSK modulation to satisfy a GSMspectrum mask criteria.